NBS SPECIAL PUBLICATION 400-9

U.S. DEPARTMENT OF COMMERCE / National Bureau of Standards

or Measurement Tech

ARPA/NBS Workshop II.

Hermeticity Testing for

Integrated Circuits
NATIONAL BUREAU OF STANDARDS

The National Bureau of Standards' was established by an act of Congress March 3, 1901. The Bureau's overall goal is to strengthen and advance the Nation's science and technology

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Semiconductor Measurement Technology:

ARPA/NBS Workshop II.

Hermeticity Testing for Integrated Circuits

Harry A. Schafft

Electronic Technology Division

Institute for Applied Technology

National Bureau of Standards

Washington, D.C. 20234

This activity was supported by

The Defense Advanced Research Projects Agency

under ARPA Order 2397, Program Code 4DiO

and

The National Bureau of Standards Washington, D.C. 20234

U.S. DEPARTMENT OF COMMERCE, Frederick B. Dent, Secretary

NATIONAL BUREAU OF STANDARDS, Richard W. Roberts, Director

Issued December 1974
National Bureau of Standards Special Publication 400-9

Nat. Bur. Stand. (U.S.)', Spec. Publ. 400-9, 43 pages (Dec. 1974) CODEN: XNBSAV

U.S. GOVERNMENT PRINTING OFFICE

WASHINGTON: 1974

For sale by the Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402 (Order by SD Catalog No. C13.10:400-9). Price $1.00
PREFACE

The Semiconductor Technology Program serves to focus NBS efforts to enhance the

performance, , interchangeability , and reliability of discrete semiconductor devices and

Integrated circuits through improvements in measurement technology for use in specifying

materials and devices in national and international commerce and for use by industry in

controlling device fabrication processes. Its major thrusts are the development of carefully

evaluated and well documented test procedures and associated technology and the dissemination

of such information to the electronics community. Application of the output by industry will

contribute to higher yields, lower cost, and higher reliability of semiconductor devices.

The output provides a common basis for the purchase specifications of government agencies

which will lead to greater economy in government procurement. In addition, Improved measurement technology will provide a basis for controlled Improvements in fabrication processes and

in essential device characteristics.

The Program receives direct financial support principally from three major sponsors:

the Defense Advanced Research Projects Agendy (ARPA),* the Defense Nuclear Agency (DNA),^

and the National Bureau of Standards (NBS).^ The ARPA-supported portion of the Program,

Advancement of Reliability, Processing, and Automation for Integrated Circuits with the

National Bureau of Standards (ARPA/IC/NBS) , addresses critical Defense Department problems

in the yield, reliability, and availability of integrated circuits. The DNA-supported

portion of the Program emphasizes aspects of the work which relate to radiation response of

electron devices for use in military systems. There is considerable overlap between the

Interests of DNA and ARPA. Measurement oriented activity appropriate to the mission of NBS

is a critical element in the achievement of the objectives of both other agencies.

Essential assistance to the Program is also received from the semiconductor Industry

through cooperative experiments and technical exchanges. NBS Interacts with industrial users

and suppliers of semiconductor devices through participation In standardizing organizations;

through direct consultations with device and material suppliers, government agencies, and

other users; and through periodically scheduled sjnnposia and workshops. This report describes

the results of the second workshop in the ARPA/NBS workshop series. In addition, progress

reports are regularly prepared for Issuance in the NBS Special Publication 400 sub-series.

More detailed reports such as state-of-the-art reviews, literature compilations, and summaries

of technical efforts conducted within the Program are Issued as these activities are completed

Reports of this type which are published by NBS also appear in the Special Publication 400

sub-series. Announcements of availability of all publications in this sub-series are sent by

the Government Printing Office to those who have requested this service. A request form for

this purpose may be found at the end of this report.

Through ARPA Order 2397, Prdgram Code 4D10 (NBS Cost Center 4259555).

tThrough Inter-Agency Cost Reimbursement Order 74-811 (NBS Cost Center 4259522).

xThrough Scientific and Technical Research Services Cost Centers 4251136, 4252128, and 4254115
Semiaonduator Measurement Technology

ARPA/NBS Workshop II. Hermeticity Testing for Integrated Circuits

Harry A. Schafft

Table of Contents

Page

1. Introduction . . . . . , 1

2 . Summary 3

3. Failure Analysis and Hermeticity

3.1 IC Package and Hexmetioalty Seated-In Contaminants

(Robert W. Thomas) 4

3.2 Failure Mechanisms Related to Hermeticity; The Nature

of Leaks (M. Douglas Keene) 9

3.3 Engineering Relationship Betideen Leak Rate and

Component Life (George R. Neff) ....... 12

3.4 Discussion Period 16

4. Evaluation and Intercomparison of Leak Rate Measurement

Procedures

4.1 ]f^eight Test Method for Hermeticity Testing

(Aaron Der Marderosian and Paul Nelson) 19

4.2 Evaluation of Helium and Radioisotope Test Methods

(Ralph E. McCullough) 21

4.3 An Overview of the NBS Hermeticity Effort

(Stanley Ruthberg) 27

4.4 Discussion Period 32

5. References 35

Appendix , ., 36
Semiconduotor Measurement Technology

ARPA/NBS Workshop II

Henneticity Testing for Integrated Circuits

by

Harry A. Schafft

Synopses are presented of the six invited talks and two discussion

periods of a meeting in which 65 engineers and scientists, representing 36

organizations from private industry and government, participated. Topics

ranged from failure analysis and the nature of leaks to evaluations and

intercompar isons of bubble, weight, helium, and radioisotope tests. Underlying many of the problems discussed is the lack of a technical basis for

specifications on maximum allowable leak rates and contaminant levels; no data are available to relate leak rate to component life. Of concern is the

proliferation of test conditions which has complicated testing and test

intercomparison efforts, and has resulted, unwittingly, in testing devices

to significantly different actual leak rate criteria. Water vapor, sealedin and that which penetrates the package, is a contaminant of major concern

and the difficulties of making sufficiently accurate measurements of water

vapor were detailed. The control required in the materials and assembly

process to avoid hermeticity failure and false leak indications in ceramic,

dual in-line packages was discussed. Finally, the importance of performing

some hermeticity tests at elevated temperatures was cited.

Key Words: Bubble test; gas analysis; helium leak test; hermeticity;

integrated circuits; measurement methods; microelectronics; radioisotope

test; seals; semiconductor devices; weight test.

1 . Introduction

The second ARPA/NBS Workshop was held on March 29, 1974, at the National

Bureau of Standards (NBS) , Gaithersburg, Maryland, and was attended by 65

engineers and scientists, representing 36 organizations. The purpose of the

workshop was to define more clearly some of the problems of hermeticity

testing, to outline NBS efforts and plans in this area, and to encourage

the coordination of efforts in hermeticity test development and standardization.

The workshop was one of a series of meetings Intended to address

various semiconductor measurement technology problems. These workshops

are a part of an effort. Advancement of Reliability, Processing, and

Automation for Integrated Circuits with the National Bureau of Standards,

sponsored by the Defense Advanced Research Projects Agency (ARPA) . This

effort is a major element of an NBS program which seeks to develop, and

to disseminate to the electronics community, carefully evaluated and well

documented test procedures and associated technology to solve measurement

workshop

purpose

workshop series

ARPA/NBS Program
and standardization problems in connection with the manufacture, procurement,

and application of semiconductor devices.

measurement Severe measurement problems with hermeticity testing had been cited in

problems

NBS contacts with a cross section of the electronics community and subsequently in an earlier ARPA/NBS workshop on Measurement Problems in Integrated

Circuit Processing and Assembly [1]. The major problems expressed were the

lack of measurement correlation for the same test method at different

stations and for different test methods at the same station, the discrepancies in the theory on which standards for test procedures are based, the

subjective nature of some preferred test procedures, and the scarcity of

definitive data linking leak size to device failure.

workshop format NBS work on hermeticity was begun in response to these measurement

needs. The workshop, which represents one part of this work, featured

morning and afternoon sessions each with three invited talks and one extended

discussion period. The morning session concentrated on failure analysis and

hermeticity while the afternoon session focused on the evaluation and intercomparison of leak test methods and procedures.

synopses Following the next, and summary, section are synposes of the invited

talks and discussion periods, which constitute the last two sections of

the report. The synopses represent the work and opinions of the speakers,

who have examined and approved them.

While detailed descriptions of the leak test method and their variations

are available elsewhere [2] [3] [4],abrief description of the generic

methods are provided here for the convenience of the reader. Five methods

are discussed or mentioned in the text, they are the helium leak, radioisotope, bubble, weight test, and penetrant dye methods. The helium leak and

radioisotope methods are similar in that both involve an attempt to force a test gas into the package through a leak. The former uses helium and the

latter uses the radioactive isotope krypton-85. The methods differ in

that the size of the leak is determined in the former by measuring the amount

of test gas, helium, that escapes from the package, and in the latter by

measuring the amount of the radioae>tive gas that is inside the package.

Bubble tests involve immersion of the package in a heated fluid and a visual

inspection for bubbles as the gas within the package expands and escapes

through the leak. Weight test methods involve the measurement of the package

weight before and after immersion of the package in a liquid under pressure

to force the liquid into the package cavity. A faulty seal is indicated by

a weight gain. Finally, penetrant dye methods involve an attempt to force

a dye into the package cavity and observing it inside the package, if the

package is transparent, or observing where it has leaked out of the package.

2
2 . Sunnnary

A basic problem which implicitly permeated the presentations and

discussions during the workshop was the lack of a technical basis for specifications on maximum allowable leak rates and contaminant levels. The reason for this is that no data are presently available which can be used to relate leak rate to component life.

A contaminant of major concern is water vapor, both sealed-in and that

which penetrates the package. Compounding this concern are the severe technical difficulties in making sufficiently accurate concentration measurements of water vapor. Specifications on sealed-in water vapor are limited

by measurement capabilities rather than device degradation considerations.

It was pointed out that because of some confusion about measurement capabilities, the maximum allowed water vapor concentration in devices in one program was set far below present capabilities to measure it. Work is

underway to establish packages with controlled concentrations of water vapor

for calibrating gas analysis facilities, and to develop a moisture sensor which can be inserted inside the package.

Of great concern, also was the proliferation of test specifications,

in particular , -for the helium and radioisotope methods. The numerous testing

conditions used lead to needlessly large numbers of tests. Moreover, they

grossly complicate intercomparison efforts and, unwittingly, result

in significantly large differences in the actual leak test criteria so that, depending on the test method used, large variations in product yield

can result. The tests specified in MIL-STD 750 and 883 were cases in point.

The causes for these differences are in part due to assumptions about the

gas flow regimes involved and in part due to the effects of pressurization

times and levels, and on internal package volumes which are not adequately

considered.

It is therefore not surprising that the need was repeatedly expressed

for standardization of test procedures and for leak rate standards which,

with possible correlation factors, could be used to standardize leak rate

rejection levels in the industry.

The nature of leaks in ceramic, dual in-line packages and the control

required in the materials and assembly processes to avoid hermeticity

failure and false leak indications, were examined in detail. Pertinent

not only to these package types is the observation that some packages which

can pass hermeticity tests performed at room temperature may fail when tested

leak rate spec^

contaminant

levels

component life

moisture

test specs proliferation

leak test criteria

differences

flow regimes

other effects

standardization

leaks in dual-in-lines

leaks at elevated

temperatures

3
bubble test

weight test method

NBS work

meeting ground

radioisotope

round robin

at elevated temperatures of from about 55 °C to 85 °C. Thus, in high

reliability applications, hermeticity tests may need to be performed

at elevated temperatures.

Through extensive use of slides and movies many shortcomings of

bubble tests used for gross leak detection were illustrated. A weight test

method developed for use on high-reliability production lines was shown

to be a sensitive measurement procedure and to be more reliable than the

bubble methods. However, because of the relatively limited number of

parts that can be tested per hour with current procedures, the method is

not presently suited for high-volume products,

NBS laboratory work and plans were outlined. In particular, work was described dealing with experimental and numerical examinations of fluid

flow mechanisms, with the development of transfer leak standards, and with

the evaluation and intercomparison of various test methods now in use. NBS participation in the ASTM round robin experiments for the helium leak

test method was mentioned.

Overall, the workshop served as a meeting ground for workers in the

field where problems and plans for the future could be discussed. Of

paramount concern were basic deficiencies in measurement methods and

technology. An immediate result of the workshop was the recognition, by

a number of the attendees, of the need for a round robin intercomparison

experiment on hermeticity testing by radioisotope methods, and the decision

to organize and participate in such a round robin under the auspices of

ASTM Committee F-1 on Electronics.

3 . Failure Analysis and Hermeticity

3.1 IC Packages and Hermetically Sealed-In Contaminants (Robert W. Thomas*)

topics discussed This presentation included a brief description of the system developed

by the Rome Air Development Center (RADC) to measure the gas ambients

inside device packages, a discussion of some of the technical problems

involved in making these measurements, a review of what has been found

inside packages assembled by different vendors, and discussions of

failure modes caused by the presence of water vapor, of the implications

of allowing epoxy materials inside packages, and of using epoxies for die

attachment

gas analysis The system used for measuring internal package gas ambients

system

includes a quadrupole mass spectrometer, a data analyzer, and a package

Code RBRM, Rome Air Development Center, Griffiss Air Force Base, New York 13441,

4
opener [5]. The last includes an ultra-high vacuum oven for baking out the

packages prior to opening. The package-opener chamber is able to acconmiodate

20 device packages. A block diagram of this system is shown in figure 1. A

capacitance manometer is used to measure the total pressure inside the package

opener at the time the package is punctured. From the pressure rise, it can

be determined if the package has a fine or gross leak. A gross leak is

indicated by no increase in pressure. A ballast is used for testing packages

with large internal volumes. The gas from the ballast can be bled off

gradually and thereby not overload the mass spectrometer.

After inserting the devices into the test chamber, the chamber is

evacuated using a turbo molecular pump. The packages are kept under vacuum for 24 hours or longer at a temperature of 125 °C to remove extraneous

contamination on the walls of the chamber and the packages. The ion pump

in figure 1 is partially choked off to minimize selective pumping when the

package is opened. The device is punctured and the mass spectrometer is

set to scan the entire spectrum of mass numbers from 1 to 100, each second.

The data analyzer automatically performs digital filtering and background

subtraction, computes and applies sensitivity factors, identifies peaks,

assigns mass numbers, reads intensities, time integrates the total gas evolved

from the package, and finally produces a hard copy of the package ambient

analysis. This is all done in a matter of seconds.

system operation

TURBO

MOLECULAR PUMP

MASS

SPECTRO. CONTROL

DATA ANALYSIS SYSTEM

ION PUMP

CRT

DISPLAY

HARD

COPY

Figure 1. Gas analysis system.

5
system

sensitivity

moisture and failure

measurement

problems

moisture

background level

high temperature

required

high conductance

needed

time integration measurement

moisture

absorbed

With this system an analysis of concentrations as low as 0.1 percent can be guaranteed and trace components down to 1 ppm can be identified.

The use of this system, since its development, has revealed that the

presence of water vapor appears to be more closely associated with device

failure than the presence of any other gas inside device packages.

However, the concentration of water vapor is exceedingly difficult to measure accurately.

Some of the technical problems in measuring the concentration of water

vapor accurately relate to establishing a sufficiently low background level

of water. In pumping and baking out the package opener chamber, each gas

is removed in a time proportional to its sticking coefficient. Water has

a particularly large sticking coefficient. To achieve the low background

level desired the chamber must be baked out for at least 24 hours.

In making the analysis of the internal package ambient it is also

important to maintain the walls of the chamber and the tubing to the

detector at a high temperature so that the gas will not become attached

to the walls and not reach the detector. To make sure that as much of

the gas ambient reaches the detector as possible it is important that

the entire system be in thermal equilibrium, that the path length between

the puncture chamber and the detector be minimized, and because such valves

are very effective filters for water vapor, that there be no fine-leak

valve between the chamber and the detector.

Another problem is that gases leave the chamber at different rates

so that a time integration of all intensities must be made to insure an accurate measure of all the gas components within the package tested. An

example of the relative rate at which different gases evolve is given in

figure 2.

An additional complication in obtaining an accurate measure of the

concentration of water vapor in the package is the presence of materials

that rfeadily absorb water such as epoxies, shellacs, and polyimides. If

such materials are present, one tends to obtain not only a measure of the

amount of water in the vapor state but also how much has been absorbed by

these materials. Actually, an indication of the water in the vapor state

at 100*C can be obtained from a time integrated over the first 5 or 10

seconds after the package has been punctured.

6
ISO

0 5 10TIME (seconds)

15 20

Figure 2. Gas evolution after package opened.

From examinations of many different package types obtained from many

different device manufacturers, it has been found that the internal package

gas ambient is unique to a given device lot. It has been possible to distinguish packages of the same type assembled by different manufacturers, and

to distinguish device lots from a given manufacturer. Gas ambient analysis can provide an iridication of the quality control exercised by the manufacturer

and can be used to monitor process improvements by examining packages from

lots made at different times. From such examinations one can also conclude

that there is no consensus in the industry regarding the best gas ambient for

package interiors.

When the manufacturer is successful in controlling the gas ambient, the

major constituent is nitrogen, the water concentration is typically less than

150 ppm, that of oxygen is less than 1 ppm, and most of the other gas

constituents are less than about 500 ppm. When he is not successful, much

higher concentrations of water vapor and oxygen are found and significant

concentrations of organics are present.

The possibility of inducing temporary leaks in ceramic packages during

high-temperature stress tests has been confirmed. This was done by subjecting suspect packages to hot (150°C) and room-temperature neon under pressure

(90 psi"). It was found that neon could be injected only under the heated

1 psi = 6804.4 Pa

package gas amblents

used to distinguish lots

constituent ^ases

temporary leaks

7
burn-in tests

hybrid devices

materials

Inside packages

moisture

specs on moisture

well-sealed

packages

conditions. The inference is that differences in the thermal coefficient of

expansion of the lead frame and glass seal can introduce sufficient stress in

marginal seals to allow a leak at elevated temperatures

Analyses also revealed that high-temperature burn-in tests alter the

gas ambient inside the package. Such tests have resulted in, for example,

increases in the hydrogen concentration, decreases in the concentration of

water, and increases or decreases in carbon dioxide.

Experience with large hybrid devices is that manufacturers of such

devices appear to feel that less care need be taken with such devices than with

monolithic integrated circuits in regard to what can be incorporated inside

the package. A case was cited in which a particular group of hybrid devices was failing due to the delamination of chip capacitors caused by excessive

moisture in the package. Analyses showed that the gas ambient had an excessive concentration of water. This was despite the precautions the

manufacturer had taken in general handling, in baking out the packages, and

in back filling the packages with pure nitrogen that was regularly monitored.

However, the manufacturer had used a water soluble flux in sealing the package

and had used inside the package such material as tape and shellac which

readily absorb water.

This is just one example of the damage that water can cause if present

in sufficiently large concentrations. It is not yet possible to define

objectively a concentration at which degradation will occur but it is felt

that it will be possible to do so soon. The Air Force Space and Missile

Systems Organization (SAMSO) has recently incorporated an RADC recommended

upper limit of 500 ppm of water vapor inside packages for devices purchased

on a sensitive high-rel space program. Such a limitation will lead to greater

reliability and 500 ppm is a reasonable level, one to which four or five

laboratories in the country can measure. However, a lower limit may be needed

for devices that are very sensitive to the presence of water vapor, such as MOS devices and devices with poorly passivated, thin film resistors.

It is possible to seal packages well enough to maintain a low level of

undesirable trace gases, such as water vapor, over long storage periods. This was demonstrated in tests of Apollo logic circuit devices, enclosed in

ceramic, glass-sealed packages in 1965 and 1966 [5]. Unusually high background

levels of hydrogen ('^1%) and helium ('^ 0,5%) were found in these devices,

however. The hydrogen is believed to be the result of outdiffusion from metal

parts during the period that the components had been baked, prior to final

sealing. The helium is believed to have diffused through the glass bottom of

these packages

8
Some concern was expressed about the uncertain effects of hydrogen on wire bonds. Hydrogen may significantly degrade wire bonds at elevated temperatures but more work needs to be done to determine if and under what

conditions such degradation can occur. The Apollo devices were not subjected

to high temperatures where the wire bond might have been affected by the

presence of hydrogen.

The results from a contract [6] involving the evaluation of a variety

of epoxies for packages and for die attachment indicate that the epoxies have

a large water content. Analysis of the internal gas ambient of devices with

such epoxies showed from 1.9 to 2.3 percent water vapor. The existence of

such high levels of water casts doubt on the appropriateness of their use

in high reliablity devices where the presence of water vapor can cause degradation.

The importance was underscored of establishing maximum allowable levels

of water vapor in the internal package ambients based on the sensitivity of

the different device classes to the presence of water vapor. This work has

been hampered by the difficulty in making precise water vapor measurements.

Accordingly, work has begun at RADC to establish packages with controlled

concentrations of water vapor to be used as standards which could be used at the different gas analysis facilities to calibrate their equipment.

Such a standard is needed because of the poor agreement between the

different facilities in the measurement of water.

Also, there is. a need for a cheaper method for determining the control

of the gas ambients within packages than the system now in use to do that.

The test of a single device now costs about $85. A contract [7] was recently

let to develop a method to insert a sensor in packages and, on a lot sampling

basis, establish that the gas sealed in the packages contains less than a certain

quantity of water.

effect of hydrogen

epoxies In packages

specs on moisture

water vapor concentration

standards

moisture sensoirs

3.2 Failure Mechanisms Related to Eermetiaity; The Nature of Leaks

(M. Douglas Keene*)

The causes for and the nature of the leaks that can occur in ceramic,

solder-glass dual-in-line packages were reviewed. The reason for limiting

the scope of the talk to this package type was the contention that this type

is presently used for over 95 percent of all hermetic integrated circuits sold

in the world and that it will continue to be the primary hermetic package in

the marketplace for the foreseeable future. An estimated 30 million such

packages are assembled each month in the United States.

leaks in ceramic

packages

Fairchild Semiconductor, IC Division, 464 Ellis Street, Mountain View, California 94040
sealing processes

causes for failure

process control

sealing

temperature

too high

frame-attach

temperature too low

seal materials

In preparation for discussing the causes for seal failure, the processes

involved in sealing this type of package were outlined. The glass used to seal together the metal lead frame and the ceramic base and cap is introduced

as a slurry mixture of vitreous glass beams suspended in an organic binder.

In general, the sealing process involves the heating of this mixture in a way

which allows the organic binder to evaporate and the glass to transform

from its initial vitreous or liquid state to a devitrified or crystalline

state. In particular, the devitrification process begins with an initial

heating in a belt furnace of the ceramic base with the lead frame resting

on a slurry layer of glass beads and organic binder. The glass melts, the

binder begins to burn off, and the frame sinks into the glass and becomes

partially bonded to the base. Devitrification of the glass, which begins

during this process, continues during the subsequent semiconductor die

attachment process which involves a glass to metal eutectic bond made at temperatures as high as 425°C. After wire bonding and visual inspection,

the ceramic cap is put in place and final sealing is performed at a temperature in the range from 450 to 525°C.

The causes for seal failure derive from inadequate control over these

processes and from improper handling. Inadequate control of the heating

process and of the quality and the mixture ratio of the glass and binder can result in a defective seal. If the sealing process exposes the glass to too high a temperature, the organic binders will not burn off before the

glass devitrifies. This can result in gases frozen into the seal in small

bubble-like cavities. Structurally weak seals, which may be porous, can also result. Such excessive temperatures could occur, for example, if a furnace belt stopped due to a power failure, if a base were left too long on a heater block in preparation for die attachment, or if the die attachment process were too slow.

Cavities and porous seals can also occur if the temperature at which

the frame is attached to the base is too low. In this case the glass under

the frame does not outgas sufficiently. Blow holes can then result during

the final sealing operation due to the build-up of gas pressure. Such

insufficiently high temperatures could be caused, for example, by increasing

the furnace belt speed in order to shorten the processing time.

Care must also be exercised in controlling the seal materials. Too

high a concentration of the binder can result in its not being burned off

during the sealing process. The glass mixture must also be evaluated to make sure that it does not exhibit any abnormal devitrification behavior.

For example, some lots of glasses have exhibited a partial devitrification at an abnormally low temperature which has prevented the complete removal of

10
glass additives

handling

placing

the binder during the sealing process. The use of differential temperature

analysis [8] on incoming glasses now helps to eliminate this problem.

Another potential problem with the incoming glass is that additives

designed to adjust the thermal expansion coefficient may not be in the

proper balance. Packages made with such glasses may fail later in temperature cycling tests. Such glasses can be eliminated in incoming inspection

by making thermal expansion tests.

Inadequate control over the mechanical handling of packages can result in the degradation of well-made package seals. Excessive physical

stress on the package leads can be transmitted to the brittle glass seals.

A number of examples of handling procedures where excessive stress could be

applied were cited: lead clipping; lead flexing, to facilitate or perform

socket insertion; and package dropping, such as might be experienced in

automatic handling and in bulk loading.

Some electro-tin plating processes used to bright-finish the external

lead frames of the sealed packages can also cause leaks. Acids used in this

process can deplete the glass, particularly adjacent to the frame. Such

leaks are most prevalent in parts that have been exposed to plating solutions

for extended periods of time and those that have been replated, as in attempts

to strip and replate tin-plated leads that oxidized during burn-in tests.

Finally, the problem of false leaks was discussed. Test methods

presently used rely on the detection of a test gas or liquid that has

penetrated the package cavity through an opening in the package seal either

while it is still inside the package (radioisotope and weight gain methods)

or as it escapes from the package (helium and bubble test methods) . Surface

porosity of the seal material, as produced by inadequate control over the seal

materials and sealing procedures, can trap the test gas or liquid and can erroneously indicate a hermeticity failure.

"False cavities" with volumes nearly as large as 10"^ cm^ can sometimes false cavities

be found in the seal material near the ends of the package, separate from the

package cavity. The amount of seal material used may be selected only on

the basis of providing a desired seal thickness in the area of the lead frame.

If too little material is used, it may happen that the surface tension of

the glass will pull the seal material towards the frame to leave a "false

cavity" at either end of the package during the sealing process. The glass

in this area may be weaker than that near the frame and package cavity and, as

a result, cracks or a porous seal may develop to provide a leak to the outside

of the package. Such a "false cavity" would give an indication of a leak

false leaks

porosity

11
indistinguishable from one to the device cavity by the helium or radioisotope

methods. To determine if a false leak exists, a dye penetrant test is used.*

False leaks, usually only seen in helium leak testing, can be caused

surface by fingerprints, pencil marks, and dirt on the surface of the device. A

contamination

single fingerprint was shown experimentally to increase an initial leak

rate reading of 10"'' atm cm^/s^ to an erroneously high level of

5 X 10~^ atm cm^/s. A solvent rinse followed by a high pressure air blast

after helium pressurization reduces this problem significantly. Some users have found that a 10-min bake at 100°C, following the helium

pressurization, improves the repeatability of the test and Improves the

correlation with radioisotope methods by eliminating surface adhering gases.

3.3 Engineering Relationship Between Leak Rate and Component Life

(George R. Neff"")

A summary was given of the results of an independent testing organization's experience with hermeticity testing of not only semiconductor devices

but also a great variety of other components such as lamp displays, relays,

thermoswitches , glow plugs, thermal probes, and circuit boards [9]. The

talk was prefaced with the statement that data to substantiate all of the

remarks could not be released at the workshop because this information

was the property of the customers who had paid for the work that had

been done by the organization.

Customer test requests for the semiconductor devices that have been received

and tested over the last few years are summarized in table 1. Here the ranges

of internal volumes are listed as are the leak-rate ranges and limits that

customers have specified. The primary hermeticity test method employed is

the radioisotope method; secondary methods are the helium and bubble tests.

Generally, customers are confused about what kinds of hermeticity

tests should be used and what minimum leak rate levels should be required.

One case cited Involved a customer who had brought in a number of hybrid

circuits, each costing several hundred dollars, with no instructions other

than that they should be tested for hermeticity.

testing

experience

customer test requirements

confusion over

tests

See footnote on page 32

j- See footnote on page 14

Iso Vac Engineering, Inc., 6220 San Fernando Road, Glendale,

California 91201.

12
Table 1. Summary of Customer Requests

Type Internal Leak rate ranges and limits of tests Percent of type Test Volume requested by customers received tested Specification

for herm^tlcity

Gross Fine Wet

cm 3 atm cm3/s atm cm3/s atm cm3/8

IC's^ 10-3 to 10-1 10-3 to 10-8 10-8 10-1 to iQ-S 40 7502/8833 Diodes 10-5 to 10-1 lO-** to 10-8 10-9 10-1 to 10-5 35 750/TX'* Transistors 10-3 to 10-1 10-** to 10-8 10-7 10" 1 to 10-8 75 750/883

Hybrids 10-1 to 10 10-3 to xQ-6 10-8 10-1 to 10-8 75 750/IV5 Plastics^ 10-3 to 1

10-** to 10-8 10-7 10" 1 to 10" 5 35 IV/ 750

1 Integrated Circuits ''MIL-STD 19500/286B ^MIL-STD 750 [2] ^ISO Vac generated specification which is usually some modification

3mIL-STD 883 [3] of the specifications in MIL-STD 750 and 883. 8cavity-type

In addition to the hermeticity test procedures given in MIL-STD 750 [2] and MIL-STD 883 [3], or combinations of the two, it has been very useful to perform the tests at elevated temperatures of from 55 to 85°C, representing

the operating temperature range of many devices. It has been found that some devices which pass fine leak tests performed at room temperature, fail

when tested at higher temperatures. Such leaks are apparently the result

of weak seals which fail under the stress resulting from differences in

the thermal coefficients of expansion of the constituent parts of the

seal. This behavior is not restricted to one package type but rather

has been found in a wide variety of package types.

Of greatest concern to customers is the presence of moisture in the

package; of somewhat less concern is the presence of oxygen. At the same

time, however, there are no data to iiidicate at what concentrations moisture

has an adverse effect on a device. A number of experiments have been

performed by workers in the field in attempts to determine such critical

concentrations but they were not successful.

A consensus is believed to exist among investigators in the field

that there is a relationship between the relative concentrations of oxygen

and water that will penetrate a package, and that the ratio of oxygen to water is about 7:1. [See Section 3.4 for a further discussion of the

validity of such a ratio.]

For a given internal package volume, a set of curves was shown of percent oxygen concentration in the package versus time after sealing for

different leak rates. These curves were calculated assuming molecular flow,

pure nitrogen as the initial internal gas ambient, and a normal atmospheric

condition external to the package. It has been possible to substantiate

these curves by the general procedure of first establishing a leak rate for

the package using the radioisotope method and then performing a gas analysis

at a known time after the package had been sealed. With such curves and

tests ac elevated

temperatures

moisture

reject level

moisture/oxygen

relationship

using oxygen to measure moisture

level

13
assuming the 7:1 ratio of oxygen to water one would be able to determine

the time after sealing that a given concentration of water would be

obtained for a given leak rate. Assuming further that one can agree

on a maximum level of moisture in the package that would not cause device degradation one could establish the maximum tolerable leak

rate for a desired lifetime or level of reliability for the device.

flow regimes vs. It was asserted that molecular flow equations can generally be applied

leak rate to the kinds of leaks that are encountered. The distribution of measured

leak rates for all components tested by a radioisotope method [10] at Iso Vac over the last few years is indicated in figure 3 as are the

relative number of components whose seal leaks can be described by viscous

and by molecular flow. The flow regimes were identified with a radioisotope method by measuring the concentration of Krypton 85 (Kr^^) after

successive exposures to Kr^^ under pressure. If the increase in the

concentration of Kr^^ remaining in the package is linear, a molecular regime

is indicated; while if an exponential increase is observed, a viscous regime

is indicated. Except for leak rates greater than about 10"** atm cm^/s,

most of the leaks found can be described using molecular flow equations.

Because of these results, a molecular flow regime is assumed when using

the radioisotope method. It should be pointed out that the devices tested

and represented in figure 3 are a biased sample in that they were generally

considered to be suspect by the customer who provided them. Thus, the

shape of the distribution would not be representative of all devices.

flow through If one were to theoretically examine the flow through a single hole,

channel

the molecular flow regime would apply only for leak rates less than

5 X 10~^ atm cm^/s, in obvious conflict with the results shown in figure 3. This only serves to point out that one is generally not dealing with leaks

in packages that can be described in terms of a single, well-defined hole.

molecular flow If a package leak be in the molecular flow regime then the pressure

regime decay within the package, while the package is held under vacuum.

Leak rate is generally considered to be the quantity of gas (in pressurevolume units) flowing through a leak per unit time, where the pressure on the low-pressure side of the leak has a negligible effect on the flow rate

It is implicitly assumed that the gas is at room temperature, is air, and

is at one atmosphere pressure on the high-pressure side of the leak. Leak

rate is commonly given in units of atm cm^/s (10 Pa m^/s) which is

equivalent to a mass flow rate of about 4 x 10"^

g mol/s.

14
LEAK RATE (atm cm'/s)

Figure 3. Distribution of Measured Leak Rates

Leak Rate Range Percent of Total Number

(atm cm^/s) of Leaking Parts Tested

10-3 to 10- 10%

lo-'* to 10-5 30%

10-5 to 10-6 0/ 50%

10-6 to 10-^ a. 6%

>10-3 , <io-^ 4%

of All Devices Tested

obeys very closely, the relation

Pt = Po exp (-kt) (1)

where P^ = internal pressure at time t (atm)

Pq = initial pressure at time t= 0 (atm),

k = conductance/volume (s"^) and

t = time (s)

Large deviations are found if the flow regime through the seal leak is a mixture of molecular and viscous flows.

It has been possible to get good correlation between the leak rates

obtained from helium and radioisotope methods, particularly for the

larger volume devices. The procedure used is to establish a leak rate

with a radioisotope method [10] using Kr^^^ assimiing molecular flow, and

then correct the reading to a helium equivalent. The package is checked

with a helium mass spectrometer for any residual helium. If none is found,

the package is pressurized with helium for a time to allow a 10 percent

concentration of helium within the package. This time is calculated as indicated in MIL-STD 883, using the helium equivalent leak rate obtained

from the radioisotope method. Correlation is established if the leak

rate measured by the helium leak test is as predicted. If there is particular

concern about the flow regime an experiment may be performed to see if the

pressure decays as predicted by eq (1)

It was pointed out that eq (1) applies only for non-sticking gases and

so does not apply to water vapor. The presence of appreciable concentrations

of moisture also makes the measurement of leak rates more difficult. Kr®5

does not penetrate or flow out of a package with a leak in a predictable way

if appreciable moisture is present. In fact, moisture can plug leaks. And,

for this reason, a dry radioisotope test must be performed before a wet one.

correlation - helium and radioisotope

tests

moisture and

leak rate measurements

15
moisture

absorption

gas' analysis

problems

need for baking

gas-analysis

system

bake-out

economics

moisture sources

A problem also occurs in the leak detection and internal gas analysis

of devices where the package material absorbs appreciable moisture before

encapsulation. In this case, the moisture that evolves from the material

can block the entrance of the Kr^^ leading to a misleadingly low leak

rate unless unusually long pressurization times are used. Also, the

moisture absorbed by the package material requires some time to evolve

into the package cavity. Thusj if a gas analysis is performed soon after

encapsulation, which is usually the case, a misleadingly low concentration

of moisture is measured.

3.4 Discussion Period

In response to a question about concentrating gases for analysis,

Thomas pointed out that gas analysis must be done in a dynamic system.

Gases from inside the package cannot be stored or concentrated because

they cannot be differentiated from the gases evolving from the package

and the wall of the analysis system. Evidence of the complex dynamic nature

of such measurements is that an initial decrease in the concentration of water

vapor may be observed upon opening the package. This results from a temporary decrease in the background level of water vapor caused by an increase

in system pressure with the opening of the package which in turn decreases

the outgasing of water from the stainless steel walls of the test chamber.

Thomas was questioned about the need to bake out his system and make

measurements with the analysis system at a high temperature. He replied

that such high temperatures are necessary in order to reduce the background

level of water vapor in his system in a reasonable time so that the

required measurement sensitivity can be achieved. He added that he usually

must bakeout the system for 24 to 48 h to reduce the water vapor background

sufficiently. The system is baked at 125'C, The temperature is reduced to 100°C during measurements.

The long bake times mentioned by Thomas elicited some cautioning

remarks about the need for practical test methods keyed to the requirements

of large scale production. For example, if a test requires bake times of

24 to 48 h this requirement would be incompatible with the need to produce parts costing only pennies a part. Thomas replied that if used

as a sample test method, such a test might be economically feasible.

In response to a question about the sources for the moisture found

in packages, Thomas pointed out that not only are the walls of ceramic

packages a sink for moisture which later serve as a source after

encapsulation but that there are other less obvious sources present.

16
While packages may be encapsulated in a dry box with a moisture content of a few parts per million, the moisture concentration in the encapsulated devices

may be as large as a few thousand parts per million. This can happen if, for

example, the tubing through which the sealing gas passes gives off moisture.

If left stagnant for 4 to 8 h, sufficient water may penetrate nylon and plastic

tubing or outgas from stainless steel tubing to contaminant the package ambient.

To minimize moisture content one needs to have dynamic flow conditions. Thomas

added that some dry boxes are supplied with neoprene gloves which allow the

moisture from the operator's hands to pass easily into the dry chamber; gloves

made of butyl rubber do not allow water penetration.

Besides degradation to thin film resistors, a questioner asked if there were any other effects that water would have on a device, Thomas mentioned a paper by Nagasime et al. [11 J which showed that for glass passivation with a concentration of phosphorus in excess of 8 percent, the presence of moisture

at 120°C for 4 h had the effect of removing the phosphorus from the glass

leaving behind a matrix in the glass that would absorb moisture and releasing

sodium atoms that the phosphorus glass was intended to getter.

In regard to performing low-temperature electrical tests it is important

to be aware that the rapidity of cooling can affect test results. Thomas

mentioned that if the package is cooled too rapidly, any moisture present in

the package may condense and freeze on the walls of the package. Thus, much

less degradation of the electrical parameters of the device may be seen than

if the cooling is performed more slowly to allow more moisture to condense on the semiconductor die.

A member of the workshop mentioned that all his experience with the

various analytical laboratories in the country has led him to the conclusion

that all analyses of the concentration of water vapor in packages by these

laboratories are "not worth a plugged nickel." It is for this reason that

he felt the 7:1 ratio of oxygen to water vapor, that Neff mentioned, was potentially so important and should be documented

Thomas disagreed with the contention that the measured concentration

of oxygen can be used as a measure of the amount of moisture in a device

package. He seldom sees small quantities of oxygen with his gas analysis

system. A reason for this is that hydrogen is the major residual gas

present in a thoroughly baked oiiit system. Hydrogen reduces the metal com- ponents so that if a package with a small quantity of oxygen is opened, the

oxygen will strike the high temperature walls, form an oxide, and never reach

the detector. Unless there exists a concentration of at least a few percent of

moisture-Induced

degradation

low-temperature

tests and moisture

analysis for moisture

relation between

moisture and oxygen

17
more on moisture

and oxygen

leak valves

moisture sensors

measurement

standards needed

present reject

levels arbitrary

life tests and leak rates

diffusion of water vapor and other gases

oxygen in the package, no oxygen will be measured. He added that even

for packages sealed in open air, they never find more than about 5 percent

oxygen with their gas analysis system.

Neff responded by saying that the 7:1 ratio was actually based on theoretically and empirically derived equations that predict such a ratio.

He mentioned that people have attempted to experimentally verify this

ratio but, in his opinion, have thus far been unsuccessful. He added

that they could have chosen another gas for which another ratio would

have been obtained. Oxygen was chosen because some feel it is detrimental

to devices.

Thomas has found that in his mass spectrometer analysis system, he is

not able to predict the calibration of leak valves for different gases

based on any parameters that can affect passage through the leak. He

finds that he must resort to empirical means.

Considering the many serious problems of making accurate analyses

of gas ambients in packages, Thomas suggested an alternative approach. A

suitable sensor could be placed inside the package to measure the moisture

sealed in and determine the level of moisture penetration for packages

with different leak rates. Using this approach, one could obtain an indication of what leak rates to test for to be assured that no significant

amount of moisture can enter the package in a given time. RADC is, therefore,

looking for some sensor that can reproducibly and quantitatively measure

the amount of water vapor in the package.

Neff reiterated his frustration at the lack of any standardized

leak rate specifications. A member of the audience added that he had

found no rationale for the leak rates specified in MIL-STD 883. It appeared, he said, that the levels were essentially arbitrarily chosen

rather than selected on the basis of fundamental considerations regarding

reliability, component life, etc.

Keene mentioned some reliability studies that he performed involving

long term life tests (10 kh) at elevated temperatures of devices with

known leak rates of from 10"'+ to 10-8 at-m cm^/s. He found significant

device degradation for the devices with leak rates in the 10"^ to 10"^ atm cm^/s range.

Ruthberg mentioned the results of some preliminary calculations

of the time it would take for water vapor to diffuse through tubes of

18
various radii and for different ambient temperatures. The results indicated

a strong temperature dependence for the diffusion coefficient and that it

might take years for moisture to enter a package through a leak channel

while it would take only seconds for a test gas such as helium or Kr^^ to do the same. Thus, for some leak sizes for which packages would be rejected,

the time for water vapor to diffuse into the package would be many times the

expected life of the device.

A basic question that needs answering, concluded Ruthberg near the end

of the discussion period, is what can leak rate measurements such as are now leak rates and being performed really indicate about the reliability of the devices being reliability

tested. Also, should one expend efforts to determine true leak rates or should one attempt to relate the behavior of the device with the results

that are obtained for one of the methods now used.

4. Evaluation and Intercomparison of Leak Rate

Measurement Procedures

4.1 Weight Test Method for Hermetiaity Testing (Aaron Der Marderosian*and Paul Nelson*)

By way of documenting the need for a better test method for gross leaks gross leak tests that led to the development of the weight test method, early efforts with

a variety of bubble test methods were described. These tests were to detect bubble tests gross leaks in devices to be used by Raytheon in the Apollo space craft and

the Lunar Excursion Module [12]. Using calibrated capillary leaks and packages

with various sized holes, the problems of subjectivity and the selection of

leak criteria for bubble tests were shown with extensive use of slides and

movie film. The primary faults of these tests are the inability, at least on

a production line, to detect packages with gross leak rates (greater than

about 10~2 atm cm^/s) and the tendency to reject too many non-leaking packages.

The need for a more reliable method for detecting gross leaks led to the

development of the weight test method. The method, in brief, consists of weight test weighing the device before and after being pressurized in a test liquid; the

leak criterion is a package weight gain of more than 1 mg after removal from

the test liquid.

The method has been found to be satisfactory for testing devices with use of weight

o test leak rates in the range of 5 x 10 ° to 10 atm cm^/s. Metal packages with

intentionally made holes to cover a range of leak rates were used to test the

effectiveness of the method. A group of 25 such packa,ges and 10 nonleaking

packages has been introduced into device manufacturer lots to audit the

Raytheon Co., 528 Boston Post Road, Sudbury, Massachusetts 01776

19
standard production line leak testing procedures. For a sequence of

42 lots including a total of about 150,000 parts, only one leaker was accepted but that was due to an operator calculation error. Since then

the test system has been automated to avoid such operator errors.

test procedure The weight test procedure was described as follows:

1. Clean devices by dipping them in clean filtered Freon TF for at

least 2 min.

2. Bake devices for 30 min in an oven preheated to 125°C (to remove

any Freon that may have gotten inside the package)

3. Weigh each device on a balance that automatically categorizes in

0.5 mg increments. (This procedure can be operated at a rate of

about 10 parts per min.)

4. Place devices in a combination vacuum-pressure vessel and reduce

pressure to less than about 1 Torr (1.3 x 10^ Pa) for 1/2 h.

5. Introduce, at the reduced pressure, FC-77 fluorocarbon liquid to submerge devices . Then slowly increase pressure to 100 psig

(-v 6.9 X 10^ Pa) and maintain it for 2 h.

6. Reduce pressure to room pressure in vessel, remove devices, and

store devices under FC-77 fluorocarbon at room pressure. Transfer

time shall be less than 1 min.

7. Remove ten devices of the same weight category from the FC-77

reservoir and allow to dry for 2 min.

8. Weigh each device and determine weight category. All ten devices

must be weighed within 4 min after removal from the reservior . (This

time limitation is to detect package with gross leaks and those

with crack-like openings through which the test fluid can quickly

flow out of the package by capillary action.)

9. Separate all devices that deviate more than two weight categories.

Reject any such device that shows a gain in weight. Recycle any

such device which shows a weight loss.

Certain commercial materials are Identified here in order to adequately

specify the experimental procedure. In no case does identification imply

recommendation or endorsement by the National Bureau of Standards nor does

it imply that the material identified is necessarily the best available

for the purpose.

20
Particulate contamination of the test fluids was mentioned as a problem.

To reduce this problem the fluid is recycled through a l-pm particle filter. A

dryer, consisting of activated alumina, was also added to remove any water

present in the test fluid. To eliminate another problem, a plastic disc is

floated on the test fluid in the vacuum-pressure vessel of step 4. This

is done to avoid the absorption into the test fluid of the nitrogen gas used

in achieving the pressure in step 5. Absorbed nitrogen causes the test fluid

to effervesce during depressurization and push out some of the fluid that may

have entered the package.

A method, developed by workers at Westinghouse, was mentioned briefly,

and described as being as sensitive as the weight test method. This method

consists of exposing the package to alcohol under pressure and then measuring

the surface conductance between internal leads. Concern was expressed,

however, about using in such a test a fluid which could conceivably degrade

devices which may have passed the leak test yet have had a trace of the

fluid enter the package.

4.2 Evaluation of Heliim and Radioisotope Methods (Ralph E. McCullough*)

This report emphasized the variability of results obtained when various

semiconductor device packages are tested for hermeticity with the helium and

radioisotope methods under the different t^st conditions specified in MILSTD 750 [2] and MIL-STD 883 [3]. The differences in the test conditions

specified in the two military standards, presented in table 2, were reviewed

Table 2. Test Con Itions of MIL-STD 750 and MIL-STD 883 for

(A) the Helium Method and (B) the Radioisotope Method

A. Helium Method

Standard Package Volume Pressurization Leak Rate Reject Level Time Pressure Indicated Calculated

cm^ h psig^ atm cm^/s atm cm^/s

MIL-STD 750 all 4 60 ± 5 5 X 10-3 HA MIL-STD 883 < 0.1 1 60 5 X 10*3 5 X

10-'^ MIL-STD 883 >^ 0.1; <_ 10 1 60 5 X

10-'^ 5 X 10-6

B. Radioisotope Method

Standard Package Volume Pressurization Leak Rate Reject Level

Time Pressure

h psia"*" atm cm^/s MIL-STD 750 all 0.1 73.5 1 X 10-3 MIL-STD 883 all 0.2 73.5 5 X 10-3

Texas Instruments Incorporated, P. 0. Box 5012, Dallas, Texas 75222

^1 psi = 6894. A Pa; 60 psi = 4,14 x 10^ ?a; 73.5 psi = 5.07 x 10^ Pa

problems with

test fluids

another method

variability of reject levels

21
and it was shewn how these differences lead to marked differences in the

calculated leak rate rejection levels and, therefore, the number of parts

that would be rejected [13]

leak rate tests Data developed from testing devices having a wide range of leak rates were presented. Three different packages were examined each having different

internal volumes . Tested were a ceramic dual-in-line package with a volume of

0.015 cm^, and TO-5 and TO-3 metal packages having volumes of 0.086 and

1.07 cm^, respectively. The packages were vacuum baked after each test and

measured prior to retesting to assure that there was no residual tracer gas.

Leak rate histograms for the ceramic package obtained for the different

tests are reproduced in figure 4. The distribution of measured leak rates

as determined from the helium method test conditions of MIL-STD 750 and shown

in figure 4A differ considerably from that of the distribution of calculated

leak rates determined from the test conditions of MIL-STD 883 and shown in

discrepancies figure 4B. Many parts that would be rejected if the test were performed

according to MIL-STD 750 would be accepted if tested according to MIL-STD 883.

The discrepancy between the two methods is seen by using the equation in the

MIL-STD 883 method to calculate an actual leak rate from the machine reading.

test data - ceramic packages

MIL-STD-883 HELIUM

MEAN = 6.95x10"^

MIL-STD-750 HELIUM

MEAN = 3.24x10'^

10"" J10''' 10"^ RADIOISOTOPE

MEAN .85x10

Figure 4, Histograms of leak rate (atm cm^/s)

for ceramic dual-in-line packages as tested

by (A) the helium method according to MILSTD 750, (B) the helium method according to MIL-STD 883, and (C) the radioisotope method

according to both MIL-STD 750 and MIL-STD 883.

22
The 5 X 10"^ atm cm^/s leak rate reject level for MIL-STD 750 transforms to

a calculated actual leak rate of 4.5 x 10~^ atm cm^/s. This rejection

level is over an order of magnitude more severe than the 5 x 10"'' atm cm^/s

^or MIL-STD 883. The distribution of leak rates as determined with the

radioisotope test is essentially unchanged for the two pressurlzation times

in MIL-STD 750 and 883 and so only one distribution need be shown in

figure 4C.

The degree of correlation between the radioisotope and helium methods

as performed by MIL-STD 750 is shown in figure 5A while that as performed by

MIL-STD 883 is shown in figure 5B. In the latter, it was felt that there was a fairly good correlation between the two methods up to a leak rate of

about 10"^ atm cm^/s. For larger leak rates there is a large, unexplained

deviation which has been seen for many package types. In the leak rate

range where the reject criteria lie, the correlation between the radioisotope and helium is as good as it is because the pressurlzation times

and levels have been considered

correlation data ceramic packages

In the metal TO-5 package the shapes of the leak rate distributions

for the different methods and procedures were similar, as seen in the

test data - TO-5 packages

10"

S 10'

5 10-^

10

MIL-STD-750

REJECT LEVEL

'i REJECT LEVEL

,-7 ^-6

10 10 ' 10

LEAK RATE (atm cin*/s) RADIOISOTOPE

MIL-STD-883

.-6

E .7 " 10 ' E

1

<

•r- P;

B

REJECT LEVEL

REJECT LEVEL

-8 •7 -6 10"" 10 10 lEAK RATE (atm cm'/s)- RADiOiSCTOrE

Figure 5. For ceramic dual-in-line packages, leak rates measured by the helium leak

method versus those measured by the radioisotope method for test conditions specified

in (A) MIL-STD 750 and (B) MIL-STD 883.

23
histograms in figure 6. This is characteristic of results from metal-can

type packages. The lack of similarity noted in the ceramic parts is possibly

due to the porisity of the ceramic material used in those packages.

correlation data - TO-5 packages

test jdata - TO-3 packages

problem with

MIL-STD 750

For this metal package type, the correlation between the radioisotope

and helium test methods appears to be better than for the ceramic packages,

especially for the MIL-STD 750 test. The correlation data are shown in

figure 7,

Leak rate distributions for the TO-3 metal packages show a similarity

in shape although the spread in the distribution for the MIL-STD 883 helium

test is smaller than that of the others. Histogram data are shown in

figure 8. Correlation data presented are shown in figure 9.

Two problems with the helium test methods for leak rates in the large

internal volume package were pointed out. For the MIL-STD 750 procedure,

the actual or calculated reject level is 3.6 x 10~^ atm cm^/s for the TO-3

package whereas for the smaller TO-5 package it is 4.5 x 10 ^ atm cm^/s, as calculated from the equation given in MIL-STD 883 to relate instrument leak

rate reading to a calculated leak rate. Thus, there is a more restricted

test criterion for large volume packages than for small volume packages.

MIL-STD-883 HELIUM

MEAN = 3.6x10"^

Figure 6. Histograms of leak rate (atm cm^/s) for TO-5 packages with internal volume of

0.086 cm^ as tested by (A) the helium method according to MIL-STD 750, (B) the hfelium

method according to MIL-STD 883, and (C) the radioisotope method according to both

MIL-STD 750 and MIL-STD 883.

24
MIL-STD-750 MIL-STD-883

10

^10-7

10

REJECT LEVEL

I REJECT LEVEL

10'^ 10"^ 10"^

LEAK RATE (itm cfflS/t^RADIOISOTOPE

10"

5 10

10"

-7

-i - REJECT LEVEL

B

I REJECT LEVEL

10"^ 10'^ 10'^

LEAK RATE |itfn cmi/i(RADIOISOTOP£

Figure 7. For TO-5 packages with internal volume of 0.086 cm^, leak rates measured by the

helium leak method versus those measured by the radioisotope method for test conditions

specified in (A) MIL-STD 750 and (B) MIL-STD 883.

MIL-STD-883 HELIUM

MEAN = 7.9x10"^

10"^ 10'^ 10'^ 10"5 MIL-STD-750 HELIUM

MEAN = 9.6x10"^

Figure 8. Histograms of leak rate (atm cm^/s) for TO-3 packages with internal volume of

1.0 cm^ as tested by (A) the helium method according to MIL-STD 750, (B) the helium method

according to MIL-STD 883, and (C) the radioisotope method according to both MIL-STD 750

and MIL-STD 883.

25
10

-5

'k 10-

10

-7

10 -8

MIL-STD-750

REJECT

LEVEL

— REJECT

LEVEL

1 0' 10-7 10- 10-

LEAK RATE (itm cm^/ilRADIOISOTOPE

MIL-STD-883

10

-5

E

10 o

E

fS

Uii

10- <UJ

-6

REJECT LEVEL

. — REJECT

LEVEL

B

10-7 10

-6 10-5

LEAK RATE i»tm enl/tf RADIOISOTOPE

Figure 9. For TO-3 packages with internal volume of 1.0 cm^, leak rates measured by the

helium leak method versus those measured by the radioisotope method for test conditions

specified in (A) MIL-STD 750 and (B) MIL-STD 883.

problem with

MIL-STD 883

test method

correlation

standard leak needed

relevant reject

levels needed

However, if one assumes that the density of an impurity gas inside the

package such as water vapor is an important consideration for device reliability, then the more restricted test criteria should be placed on smaller

volume packages.

For the procedure specified in MIL-STD 883, the use of the 5 x 10~^

atm cm^/s reject point corresponds to an instrument reading of about

10-'* atm cm^/s which is normally beyond the range of most machines. If one uses the 5 x

10"'' atm cm^/s instrument reading reject point one really is

using a calculated reject point of 2 x 10"'' atm cm^/s. Thus, there is a choice between two reject criteria that are over an order of magnitude

different, when compared as calculated or as indicated readings.

In summary, it is possible to obtain good correlation between the helium

and radioisotope test methods in the range of interest. However, to do this

it is necessary to take into consideration that the leak rate indications on helium leak test instruments are dependent on internal package volumes and

on pressurization levels and times. Furthermore, there is a desperate need

for the development of standard leak packages of known volume and leak rate

with which to calibrate systems not only with regard to the instruments'

indicated leak rates but with regard to the pressurization levels and times.

Another need is to decide what leak rate reject levels are relevant and

appropriate for reliability arid life requirements of devices.

26
4.3 An Overview of the NBS Hermetiaity Effort (Stanley Ruthberg )

This talk began with a listing of five elements which are or will be

included in the NBS effort. They are (1) an examination of fluid flow

mechanisms by both numerical and experimental analyses for particular

geometries and pertinent fluids, (2) the development of transfer leak

standards, (3) an evaluation and intercomparison of measurement methods,

(4) the application of guidelines developed from the first three elements

for theoretical models to real packages with real leak channels, and (5)

the development of new measurement methods. The primary efforts at NBS

currently involve the first three of these elements and they were discussed

in the talk.

NBS work

In the discussion of fluid flow mechanisms it was shown that without

reference to gas flow models no correlation can be made between the measured

and true leak rates. It appears that part of the reason for poor correlation

between the helium and the radioisotope methods is the use of equations that are not all derived for the same gas flow regimes. To illustrate the effect

of assuming different gas flow models for the helium leak test, pldts of true versus measured leak rates for the helium leak test derived by two groups and

for both laminar and molecular gas flow regimes are reproduced in figure 10

t

flow regimes and test methods

molecular and laminar flow

Figure 10 . Measured leak rate versus true

leak rate for laminar (LAM) and molecular

(MOL) flow regimes as determined by the models

of Howl and Mann (H/M) and of the Defense

Electronics Supply Center for the test con- ditions indicated where Pg ts Chei tracer gas

pressurization, V is the internal package

volume, T is the pressurization time, and

T is the time after pressurization that the

leak test is performed.

10' 10* 10' 10' 10' TRUE LEAK RATE (atm cmVs)

National Bureau of Standards, Washington, D.C. 20234

The indicated or measured leak rate of a package depends on, for example, the level of

pressurization and time after depressurization as the helium gas escapes from the package

which in turn affects the gas flow regime involved. The curves in figure 10 relate the

measured to the calibrated or true leak rate which is determined from a standard leak

under standard test conditions. „t
Two sets of curves for molecular and laminar flow are shown. The upper set

is from Howl and Mann [1^] while the lower set is from the Defense Electronics

Supply Center [4]. Even if the test conditions shown in the figure were the

same, there could be significant differences between the sets because of the

different assumptions made by the two groups in the derivation of these

relationships

measured and To complicate the matter of relating measured leak rate to true leak

true leak rate' rate, the actual flow regime is likely to be some mix of laminar and molecular

flow regimes. To pursue this further and to suggest how sensitive the degree

of mixing may be to the nature of the leak, the results of some preliminary

calculations were shown for expected flow regimes and for different sized

leak channels using the equation of Knudsen [15]. This equation which was originally formulated on a semi-empirical basis, gives correct behavior for

total flow rate transition flow at subatmospheric pressures. In this equation the total flow

rate, Qj (atm cm^/s)jis given by

Qt = Ql + ZQm

Where Ql is the laminar flow (atm cm^/s),

is the molecular flow (atm cm^/s), and

Z is a function of the ratio of the average mean path. A, to the radius of the leak

channel, R.

flow regimes for Flow regimes for channel leaks of length 0.1 cm but with different radii

channel leak and for two pressure differentials were considered and the results are summarized in table 3. For one atmosphere of pressure on the upstream side

of the channel, P2 , and zero pressure on the downstream side of the

channel, P]^, the flow rates vary from about 10"^ to 10~^ atm cm^/s for

channel radii from 10 to 0.1 pm. The flow regime varies from 95 percent

laminar flow for the lO-pm radius channel to complete molecular flow for the

O.l-ym radius channel. Increasing the pressure to 5 and 1 atm for P2 and P^,

respectively, shifts the flow regime toward laminar flow. This change in

pressures has, for example, changed the regime from completely molecular

flow to 50 percent laminar flow for the O.l-ym radius channel. The implication is that in the process of testing the hermeticity of a package with

such a leak where pressures Pj^ and P2 would be changing, the flow regimes

could also be changing significantly.

Additional factors affect flow. There exists a transition length, Lg,

factors affecting

flo„ or distance that the gas must flow in the channel before uniform, laminar

flow is achieved. There is also a gas flow limit, Qcomp> which compressibility effects tend to reduce the flow rate. There are other limits, Qturb

28
and Qcrit' which are the flow rates for turbulent and sonically choked flow,

respectively, which also tend to reduce the flow rate. The values for Lg,

Qcomp> Qturb' Qcrit ^o^^ leak channels 1 mm in length for different

radii and pressures ?2 and Pi are shown in table 4. For = 5 atm and a lO-pm radius channel, the transition length is greater than the length of

the channel so that laminar flow is not achieved anywhere in the channel.

Further, the flow, Qt, has surpassed the compressible flow limit, Qcomp' an order of magnitude. Even for the S-ym radius channel, Qcomp « Qt • At a more typical pressurization of 10 atm and for a 5-pm radius, is a significant

fraction of the channel length and the compressible flow limit is exceeded by

almost an order of magnitude.

Table 3. Types of flow and flow rate through cylindrical leak channel of 1 for different channel radii, R, and different upstream, P2 , and downstream,

pressures

P2 Pi R Qt Qt/Qm Ql/Qt R/ \ atin atm ym atm cm^/s

1 0 10 1.2 X 10-2 15.5 .95 100

1 0 5 9.4 X

10"'+ 8.2 '^' .90 50

1 0 1 2.1 X 10-6 2.3 '^^ .50 10

1 0 0.1 1.1 X 10-9 1.0 0 1

5 1 1 3.9 X 10-5 9.6 ^ .90 60

5 1 0.1 6.3 X 10-9 1.7 .50 6

Table 4. Gas flow rate, transition length, and gas flow limits for a cylindrical leak

channel 1 mm long for different radii, R, and different upstream, P2, and downstream, P^,

pressures.

P2 Pi R Qt Qcomp Qturb Qcrit

atm atm ym atm cm^/

mm atm cm^/s atm cm^/s atm cm-^/s

5 1 10 3.3 X 10-^ 1. 3 4 X 10-2 4.9 X 10-1 6.5 X 10-1

5 1 5 2.1 X 10-2 9. 7 X 10-3 1 X 10-2 2.4 X 10-1 1.6 X 10" 1

5 1 1 3.9 X 10-5 2. 4 X

10-'+ 4 X 10-^ 4.9 X 10-2 6.5 X 10"2

10 1 10 1.4 6. 1 4 X

10-2 4.9 X 10" 1 1.3

10 1 5 7.5 X 10-2 0. 34 1 X 10-2 2.4 X 10-1 3.3 X

10"!

10 1 1 1.4 X

10"'+ 6. 5 X

10-'+ 4 X 10-"+ 4.9 X

10"2 1.3 X

10"^

29
flow dependence All these data were calculated for air. Other gases will exhibit different

on gas leak rates and compressible flow limits. Values relative to air are shown in

tables 5 and 6. From these data it can be seen that, for example, helium can

be used at much higher pressures than air before exceeding the compressible

flow limit. Also, the leak rates can differ significantly from that of air

for different gases and that these differences may vary significantly with

channel radius. For helium gas, the leak rate relative to air changes from

about unity for a lO-ym radius channel to 2,7 for a O.l-vim radius channel.

Pure krypton 85 shows a much smaller variation while argon shows very little

variation at all.

®ther There are still more complications and some relate to the fact that so far

complications

the data presented are for one-directional flow, into the interior of the device.

The flow rate out is dependent on the internal volume, leak size, and pressurization time. Actually, the limiting effects of gas flow for gross leaks and

the possible'Hiix of flow regimes for very small leaks are academic for the

helium and radioisotope methods. It is the intermediate leak-rate range that

is of significance and should be studied carefully because it is in this range

where the reject level is located and factors of 2 or 3 in the measured leak

rate values can very significantly affect production yield.

Table 5. Transition length and gas flow

limits of He and Kr^^ relative to air.

Gas Qc Qt Le

air 1 1 1 He 2.8 8.1 0.: Kr85 0.62 0.65 1..

Table 6. Leak rates for different gas:es relative to air of 1.0-mm long cylindrical

channels of different radii.

Gas

10 ym

Channel Radius

1 ym 0.1 ym

air 1 1 1 Ar 0.83 0.84 0.85

He 1.09 1.77 2.7

H2 2.22 2.90 3.62

Kr85 0.74 0.59

30
These data demonstrate that further assessment of gas flows is needed,

both numerical and experimental. Experimental work requires the use of stable

and precise leaks for the study of both flow behavior and, when sealed to known volumes, leak rate characteristics of real packages. Measurements of

flow rates as a function of gas species and pressure conditions by mass spectrometers and manometers are being planned with instruments that are available or in assembly in NBS's laboratories. The Howl and Mann theory [13]

is now being tested for large-volume devices in a round robin conducted by

the ASTM Committee F-1 on Electronics.

In regard to transfer standards and methods for evaluating these

standards, the development of suitable test bodies is important to the

solution of many measurement problems. Not only would such test bodies, or transfer standards, be helpful in experimentally discriminating between

theoretical models, but they could allow routine and repeated checks of

leak rate measurement performance as well as Intercomparison of different

measurement stations and methods.

A suitable method for measuring flow rates is necessary for the

development of such test bodies. Leak rates greater than 10"^ atm cm^/s can be measured by a rate-of-rise technique in measured volumes with absolute

reference manometers [16]. The conductance of such leaks can then be

calculated. A combination of leaks for which the conductances have been so measured and calculated can be assembled to form a flow divider which in

turn can be used to measure leak rates in the range from 10~^ to 10~^^

atm cm^/s. In conjunction with an ultra high vacuum system and mass

spectrometer, NBS will have the capability of measuring quickly and directly

any leak for any well-behaved test gas.

An important capability of a transfer standard is the incorporation

of a calibrated leak into an envelope designed so that the resultant test

body can be used repeatedly without degradation. One possible design

for such a test body is a refinement of the type presently being used

in the round robin experiment mentioned above. The refinement involves

the use of a smaller test volume and a construction with a glass less

permeable to helium. Another possible design is shown in figure 11 where

a stainless steel tube is sealed at one end with a demountable aluminumfoil, high-vacuum seal [17] and at the opposite end could be attached to a porous plug or crimped as shown in the figure. Stable test bodies with

known leak rates measured for the tracer gas used: would allow direct

calibrations with improved precision of the particular leak test techniques

used, would allow a direct comparison of the capabilities of the

different methods in use, and could serve on the production line to

test. for measurement integrity.

more work, needed

transfer standards

flow rate measurements

calibrated leak

use of such

leaks
NUT

y

WASHER

i

X

FOIL

GASKET

OUTER

STEM

_ CRIMPED

HYPO TUBE

5mmFigure 11. Design for transfer standard

4.4 Discussion Period

data scatter Neff was concerned that the audience did not realize that the data shown

by McCullough, which indicated relatively small scatter of data points in the

plots of the helium versus the radioisotope test results, were obtained by

engineers using the test equipment under well-controlled conditions. Were

this done in a production-line environment, he noted that the scatter in data

points would be far greater. McCullough readily agreed that this was so but added that within the relatively narrow leak-rate range about the reject

level for a given package type, the difficulty in controlling conditions even on a production line was not so great.

In reference to a question from the audience, McCullough agreed that

reject levels there should be more reject levels to more finely cover the range of internal

for Helium test package volumes in use for the helium leak test.

It was pointed out that with some of the larger volume package types,

package damage the high pressures specified can result in package damage. However, if the

pressure level is reduced the sensitivity of the test method will be severely

reduced unless the pressurization times are increased to inconveniently long

periods.

Keene showed slides of a number of packages prepared with a dye to

nature of leaks define the area and extent of typical leaks found in ceramic packages.

Parts were pressurized at 100 psi (6.9 x 10^ Pa) for Ih in a fluorescein dye

diluted 10:1 with trichloroethelene and then baked after pressurization to dry

the dye.

32
Keene's purpose was to show that none of the leaks exhibited any well-defined

tubular holes. Rather, they all indicated that the leak consisted of a system

of defects or cracks in the glass or ceramic material.

Keene was asked if he has experienced many problems with the absorption

of Kr^^ on the surface of ceramic packages. He replied that one can detect surface absorption of Kr^^ by using a beta detector. However, in

actual applications where he has radioisotope and helium test instruments

next to each other, he does not have surface absorption or problems with

fingerprints, pencil marks, etc. with the radioisotope test but does with

the helium leak tester. Neff suggested that the reason for this is the

shorter pressurization times required for the radioisotope method. If

these times were as long as those in the helium leak test, surface absorp"

tion would also be a problem with the radioisotope method.

Thomas reviewed some of the anticipated changes in MIL-STD 883

relative to hermeticity tests. These changes are listed in Appendix A. One of the projected changes is to prevent gross leak testing before making

a fine leak test to avoid the possibility of plugging a fine leak. This

generated considerable discussion in that other procedures and tests, such as

a thermal shock test, could also serve to plug a fine leak. One participant summed up this part of the discussion by saying that there would be

"no peace in the family" until what is done to the part before performing

the hermeticity test is adequately specified.

Thomas also indicated that perhaps too much emphasis was being

placed on gross and fine leaks at the expense of learning what is inside

the package to start with. This became part of an extended discussion on

the role and the generation of moisture inside the package and

the need to correlate leak rates for moisture to the leak rates of helium

and Kr^^. One pointed out that they had spent much time at the workshop

talking about one problem (moisture inside the package) and measuring

another (the penetration and escape of helium and Kr^^)

These discussions led to a reiteration of the need for work to determine what levels of contaminants, such as moisture, could be

tolerated and from that establish some generally agreed upon leak rate

reject level to wh'-ch all could test to.

At the end of the discussion period and the workshop, after the

discussion had turned to essentially manufacturing and procurement problems,

McCullough reminded the participants that NBS cannot solve such problems.

Rather, he said, NBS can and should provide the industry with the measurement tools so that we will know that what we think we are measuring is

actually what we are measuring!

33

surface absorption

MIL-STD 883 changes

plugging leaks

moisture In packages

setting reject levels

NBS's role
Acknowledgement

The active participation of the speakers and the attendees, which made the workshop

a success, are acknowledged here with pleasure. Thanks go to the speakers who provided me with copies of the visual materials used in the talks and with written materials which

assisted greatly in the preparation of this report. Special thanks go to Stanley Ruthberg,

leader of the NBS hermeticity project, who served as the technical chairman of the workshop

and who provided me with technical insight that was very valuable in the preparation of the

report. I also wish to express my gratitude to W. Murray Bullis for his editorial assistance,

to Edgar C. Watts for his work with the figures, to Mary Jane Ronas for her skilled help in

proofreading the final draft, and to Ellen Y. Trager for her diligence in typing the final

and camera- copy draft.

34
References

[1] Schafft, H. A., Semiconductor Measurement Technology: ARPA/NBS Workshop I. Measurement Problems in Integrated Circuit Processing and Assembly, Nat. Bur. Stand.

(U. S.), Spec. Publ. 400-3, 24 pages (Feb. 1974).

[2] Method 1071 - Hermetic Seal, Military Standard 750B, Test Methods for Semiconductor

Devices, Feb. 27, 1970. (Available from U. S. Naval Publications and Forms Center,

5801 Tabor Avenue., Philadelphia, PA. 19120.)

[3] Method 1014 - Seal, Military Standard 883, Test Methods and Procedures for

Microelectronics, May 1, 1968. (Available from U, S. Naval Publications and Forms

Center, 5801 Tabor Ave., Philadelphia, PA. 19120.)

[4] Guidelines for Hermetic Seal Testing of Semiconductor Devices, prepared by Defense

Electronics Supply Center, Dayton, OH. (April 1, 1969).

[5] Thomas, R. W. , and Moore, B. A., Unique Reliability Analysis Capability, Proceedings

Air Force Science and Engineering Sjnnposium, Vol. 1, Kirtland Air Force Base,

Albuquerque, NM. , Oct. 1973; Air Force Systems Command (AFSC) report number:

AFSC-TR-73-003. AD 771-618.

[6] Evaluation of Adhesives for Hybrid Microcircuits , Martin Marietta, Denver, CO;,

Contract Number AF30602-73-C-0149 . For further information contact A. Tamburino

at RADC, telephone (315) 330-2813.

[7] "Microcircuits Contamination Control," Texas Instruments, Inc., Contract Number

F30602-74-C-0203.

[8] Ramsey, T. H., Use of Differential Analysis in Controlling Behavior of Solder-Glass

Seals in Ceramic Packages, Solid State Technology 15, 29-33, 43 (Jan. 1972).

[9] Stanley, A. G. , and Neff, G. R., Leak Detection of IC and other Semiconductor Devices

on Multilayer Circuit Boards, 12th Annual Proceedings Reliability Physics, 1974,

pp 239-242. (Available from IEEE Publications Sales Dept., 345 East 47th St.,

New York, NY. 10017, using IEEE Catalog No. 74CH0839-1 PHY.)

[10] Reed, C. W. , and others, Non-Destructive Method for Testing Bodies for Penetrability

by Particulate Matter, U. A. Patent 3,135,865, issued June 2, 1964.

[11] Nagasima, N. , Suzuki, H. , Tanaka, K., and Nishida, S., Interaction Between Phosphosilicate

Glass Films and Water, J. Electrochem, Soc. 121, 434-438 (March 1974).

[12] Problems with bubble tests and a description of the weight test method is given in an earlier published article: Test Editor, Reported more Reliable - Weight Test Method

Detects Gross Leaks in Components, Evaluation Engineering 1., 12-16 (Sept. /Oct. 1970).

[13] Work done under RADC contract F30602-73-C-0150

[14] Howl, D. A., and Mann, C. A., The Back-Pressurising Technique of Leak-Testing, Vacuum

15, 347-352 (March 1965).

[15] Dushman, S., and Lafferty, J. M. , Ed., Scientific Foundations of Vacuum Technique,

2nd ed., p. 106, (John Wiley & Sons, Inc., New York, 1962),

[16] Method for Vacuum Leak Calibration - American Vacuum Society Standard (tentative)

J. Vac. Sci. Techn, 5^, 219-222 (Nov. /Dec. 1968).

[17] Ruthberg, S., and Creedon, J. E. , Aluminum Foil High-Vacuum Gasket, R.S.I. 26, 1208

(Dec. J.955).

I 35
APPENDIX A

Anticipated Changes in Method 1014 of MIL-STD 883

TEST CONDITION A - Helium Fine Leak Test

Three methods will be allowed:

1. Fixed Method: Same as present method using fixed preconditioning parameters.

2. Flexible Method: Use formula to determine preconditioning parameters for

specific package cavity volume. As an alternative,

preconditioning parameters for a series of package cavity

volumes may be selected from a table.

3. Packaged in Helium Method: Use to test package sealing process.

TEST CONDITION B - Radioisotope Fine Leak Test^

Minor changes . r , .. . ,. ..

TEST CONDITION C - Fluovoaavbon Gross Leak Test

Of the two present methods, only the one requiring pressurization will be

required with some changes in the preconditioning parameters.

TEST CONDITION D - Penetrant Dye Gross Leak Test

Minor changes

TEST CONDITION E - Weight Measurement Leak Gross Test

New Test. Similar to weight test described in Section 4.1

36

1
NBS-114A (REV, 7-73)

U.S. DEPT. OF COMM. 1. IHMM.K A l lON OR Kl I'OK'T 2. Gov't Accession BIBLIOGRAPHIC DATA NBS-SP-400-9

5n E E T

3. Recipient's Accession No.

4. TI'I I.H AND sum I I LI-: Semiaonduotor Measurement Teohnology : ARPA/NBS Workshop II Hermeticity Testing for Integrated Circuits

5. Publication Date December 1974

6. Performing Organization (ode

7. AUrHOR(S) ,, „ ^ , Harry A, Schafft

8. Performing Organ. Report No.

9. F^ERt-ORMlNC, ORGANIZATION NAME AND ADDRESS

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

10. Project/Task/Work Unit No.

11. ( ontract /Grant No. ARPA Order No. 2397

Program Code 4D10

12. Sponsoring Organization Name and Gompletc Address (Street, City, State, ZIP)

Defense Advanced Research Projects Agency - 1400 Wilson Blvd.,

Arlington, Virginia 22209

National Bureau of Standards, Washington, D. C. 20234

13. Type of Report & Period Covered Final

14. Sponsoring Agency Code

15. SUPPLEMENTARY NOTES

16. AHSTRACn' (A 200-word or Jess (actual summary at mo.s f sigriificant information. If document includes a significant

bibliography or literature survey, mention it here.) Synopses are presented of the six invited talks and two discussion periods of a meeting in which 65 engineers and scientists, representing 36 organizations from private industry and government, participated. Topics ranged from failure analysis and

the nature of leaks to evaluations and intercomparisons of bubble, weight, helium,

and radioisotope tests. Underlying many of the problems discussed is the lack of a technical basis for specifications on maximum allowable leak rates and contaminant

levels; no data are available to relate leak rate to component life. Of concern is the

proliferation of test conditions which has complicated testing and test intercomparison

efforts, and has resulted, unwittingly, in testing devices to significantly different

actual leak rate criteria. Water vapor, sealed-in and that which penetrates _ the package, is a contaminant of major concern and the difficulties of making sufficiently

accurate measurements of water vaoor were detailed. The control required in the

materials and assembly process to avoid hermeticity failure and false leak indications

in ceramic, dual in-line packages was discussed. Finally, the importance of performing

;some hermeticity tests at elevated temperatures was cited.

17. KEY WORDS (six to twelve entries; alphabetical order; capitalize only the first letter of the first key word unless a proper name; separated by semicolons

Bubble test; gas analysis; helium leak test; hermeticity; integrated circuits;

measurement methods; microelectronics; radioisotope test; seals; semiconductor devices;

weiaht test.

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as the official source of information in the Federal Gov- ernment regarding standards issued by NBS pursuant

to the Federal Property and Administrative Services Act of 1949 as amended, Public Law 89-306 (79 Stat. 1127), and as implemented by Executive Order 11717

(38 FR 12315, dated May 11, 1973) and Part 6 of Title 15 CFR (Code of Federal Regulations). FIPS PUBS

will include approved Federal information processing standards information of general interest, and a complete index of relevant standards publications. Consumer Information Series—Practical information, based on NBS research and experience, covering areas

of interest to the consumer. Easily understandable language and illustrations provide useful background

knowledge for shopping in today's technological

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NBS Interagency Reports—A special series of interim

or final reports on work performed by NBS for outside sponsors (both government and non-government). In

general, initial distribution is handled by the sponsor;

public distribution is by the National Technical Infor- mation Service (Springfield, 'Va. 22151) in paper copy

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The following current-awareness and literature-survey

bibliographies are issued periodically by the Bureau:

Cryogenic Data Center Current Awareness Service

(Publications and Reports of Interest in Cryogenics).

A literature survey issued weekly. Annual subscription: Domestic, $20.00; foreign, $25.00. Liquefied Natural Gas. A literature survey issued quarterly. Annual subscription: $20.00. Superconducting Devices and Materials. A literature survey issued quarterly. Annual subscription: $20.00. Send subscription orders and remittances for the preceding bibliographic services to the U.S. Department

of Commerce, National Technical Information Service, Springfield, Va. 22151. Electromagnetic Metrology Current Awareness Service (Abstracts of Selected Articles on Measurement

Techniques and Standards of Electromagnetic Quantities from D-C to Millimeter-Wave Frequencies).

Issued monthly. Annual subscription: $100.00 (Special rates for multi-subscriptions). Send subscription order and remittance to the Electromagnetic Metrol- ogy Information Center, Electromagnetics Division, National Bureau of Standards, Boulder, Colo. 80302.
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