Serial pumping for portable handling tool of electronic workpieces

A battery-powered portable tool for handling electronic workpieces, such as semiconductor wafers, wherein a desired pressure differential is generated by a serial connection of vacuum pumps. The tool includes a number of features which minimize the generation of particulate matter. The pumps are sealed in an airtight chamber to prevent the release of particles created during operation of the pumps. The tool is exhausted directly to the ambient atmosphere to prevent pump exhaust from disturbing particles within the tool. The valve is designed to provide a quick release of even lightweight workpieces and to minimize the sliding of valve components against each other. Submicron filtering removes any particles from the pump exhaust.

TECHNICAL FIELD 
The present invention relates generally to handling tools and more 
particularly to vacuum-actuated tools for handling electronic workpieces. 
BACKGROUND ART 
Both during and between processing steps fabricating integrated circuit 
chips, various devices are utilized to handle electronic workpieces. An 
"electronic workpiece" is defined as any article that is formed during 
steps of assembling an electrical device. Such articles include 
semiconductor wafers on which a number of integrated circuit chips are 
fabricated, the individual chips following dicing of a completed 
semiconductor wafer, and integrated circuit packages containing one or 
more chips for attachment to a printed circuit board. Handling tools 
include vacuum-actuated devices to which a wand tip is removably attached. 
Air is evacuated from the wand tip to provide a force for picking up 
workpieces that are brought into contact with the wand tip. 
There are advantages to the use of portable vacuum-actuated handling tools, 
but various factors have made it difficult to manufacture a practical 
portable vacuum tool that meets the requirements of the electronic 
industry. These factors include: (1) cost considerations; (2) force 
requirements; (3) particle generation concerns; and (4) a need for rapid 
vacuum release. The first two factors are typically tradeoffs. Portable 
vacuum tools are available, wherein the tool is a two-piece member 
comprising a base having a vacuum pump and a wand handle having a valve 
and a wand tip. The base is connected to the wand handle by a hose. The 
vacuum pressure of such a tool is typically within the range of 5 to 15 
inches of Hg. While the available vacuum pressure works adequately in many 
applications, it is well below the 21 to 26 inches of Hg that is available 
using in-house vacuum systems at wafer fabrication facilities. Increasing 
the vacuum capacity within a portable electronic workpiece handling tool 
has required use of a vacuum pump that is considered cost inefficient by 
many users. 
Regarding particle generation, even minute particulate matter will 
contaminate a semiconductor wafer. Particulate contaminants on an active 
area of the wafer will lower the yield, and therefore raise the cost, of 
the manufacturing process. If the particulate contaminants are excessive, 
expensive and time consuming cleaning and inspection steps may have to be 
added to the process. Vacuum pumps in a portable handling tool include 
bushings which render the pump susceptible to particle generation. 
Consequently, great care must be taken in the design of vacuum tools for 
cleanroom operation. Fabrication facilities include in-house vacuum 
systems in which, unlike portable tools, the vacuum exhaust is released 
outside of the room in which electronic workpieces are located. For this 
reason, there is a tendency to use in-house systems and there is a 
reluctance to use portable handling tools. 
The valve on a handling tool plays an important role in the operation of 
the tool. As noted above, the valve should provide a rapid release of an 
electronic workpiece. The most common valving mechanism is one in which a 
user presses a reciprocating button or lever to cause displacement of a 
valve stem having a cylindrical shape with a circular groove cut into the 
outside surface. Movement of the button or lever aligns the circular 
groove with an axial bore through the tool, thereby providing a flow path 
for evacuation from a wand tip connected to the tool. The cylindrical 
valve stem is dimensioned to block the axial bore when the circular groove 
is not aligned with the axial bore. One difficulty with this valving 
mechanism is that a reduced vacuum pressure remains even after 
misalignment of the circular groove. Therefore, the release of a 
lightweight electronic workpiece is slowed. Another difficulty is that 
such a valving mechanism requires adherence to close tolerances in order 
to ensure blockage of the axial bore. This often requires a sliding of one 
part against another, thereby creating another source of particulate 
contamination. 
It is an object of the present invention to provide a generally 
nonparticulating portable vacuum tool for handling electronic workpieces, 
wherein the tool is cost-efficient and includes a quick-release mechanism. 
SUMMARY OF THE INVENTION 
The above object has been met by a portable battery-powered handling tool 
for electronic workpieces in which a pressure differential is created by a 
serial connection of first and second vacuum sources. Thus, the tool does 
not rely upon an expensive, high capacity single source pump arrangement. 
Particle generation is minimized by providing an airtight chamber for 
housing the serially connected vacuum sources, by exhausting the vacuum 
sources directly to the ambient atmosphere, by providing submicron 
filtering of the exhaust, and by utilizing a valve that does not require a 
tight sliding of a valve stem against surrounding structure. 
Preferably, the tool is a single piece tool having the serially connected 
first and second vacuum pumps, the valve and a battery housed within a 
portable body on which a vacuum tip is removably mounted. That is, in a 
preferred embodiment the tool is a stand alone device. Air from the vacuum 
tip is evacuated through the valve and enters an inlet of the first vacuum 
pump. The outlet of the first vacuum pump is connected to the inlet of the 
second vacuum pump. The vacuum pumps are isolated in an airtight chamber 
so that the tool is not susceptible to the generation of particulate 
contaminants normally associated with pumps. Rather than exhausting into 
the body of the tool, the outlet of the second vacuum pump is filtered and 
exhausted into the ambient atmosphere. This prevents particles that were 
created during manufacture of the tool from being disturbed and vented 
into a fabrication cleanroom. 
The valve includes a path to the atmosphere that is connected to the vacuum 
tip upon movement of the valve to a workpiece-release position. 
Consequently, no residue vacuum pressure is retained at the vacuum tip and 
a rapid release is achieved. Moreover, the vent to the ambient atmosphere 
is along the valve stem, so that the valve is not a type that requires a 
close sliding of the valve stem against surrounding structure. 
In another embodiment, the vacuum pumps and the battery are housed within 
the portable body, so body acts as a base, and a hose connects wand member 
that includes the vacuum tip and the valve. In yet another embodiment, the 
base includes an attachment for selectively securing the base to the belt 
of a user. 
An advantage of the present invention is that the attachment of the vacuum 
pumps provides a pressure differential generally equivalent to that of a 
conventional in-house system of a fabrication facility. The tools designed 
for attachment to the in-house system without exerting a pressure so great 
that workpiece breakage would occur. Another advantage is that the tool 
has been to minimize or eliminate particle generation, while allowing a 
user to conveniently relocate the tool as needed.

BEST MODE FOR CARRYING OUT THE INVENTION 
With reference to FIG. 1, a stand-alone handling tool 10 for electronic 
workpieces is shown as including a vacuum tip 12 for picking up a 
semiconductor wafer 14. The vacuum tip is demountably attached to a body 
16 of the tool. Depending upon workpiece which is to be handled, a number 
of different vacuum tips can be used. The vacuum tip 12 includes a stem 18 
that is press fit into a fitting 20 extending from the body. 
Alternatively, locking hardware may be used to secure the vacuum tip to 
the body. 
The vacuum tip 12 is made of a material suitable for the desired 
application. Applications vary in terms of chemical atmosphere and 
temperature. The material should be nonparticulating. Polyetheretherketone 
(PEEK) is a suitable material in many applications. Air is evacuated from 
a chamber 22 via an opening 24 in a vacuum tip. In order to provide 
support that will limit any deformation of the semiconductor wafer, lands 
26 extend toward the center of the chamber 22. 
The body 16 of the tool 10 is configured for easy handling. A body having a 
width of 0.75 inch, a height of 1.0 inch and a length of 1.5 inches is 
contemplated, but larger tools are also available. 
Referring now to FIGS. 1 and 2, the handling tool 10 is powered by a 
battery pack 28. A Ni-Cad rechargeable battery pack that provides a 
voltage of 7.2 V at 700 milliamp/hr may be used. An electrical jack 30 
connects to a recharging unit, not shown. 
A toggle switch 32 is utilized to energize a power lamp 34 and a pair of 
pump motors 36 and 38. Two pumps 40 and 42 are shown connected in serves 
with respect to evacuation of air from the vacuum tip 12. In order to 
achieve a greater vacuum pressure, more pumps may be connected in series. 
Preferably, the vacuum pressure is generally equivalent to that of an 
in-house system of a fabrication facility, i.e. 21 to 26 inches of Hg. 
Preferably, each pump is an oil-less diaphragm type device. An acceptable 
pump is manufactured by KNF Neuberger, which provides a single-pump vacuum 
pressure of approximately 16 inches of Hg. In connecting two such pumps in 
a parallel fashion, it was discovered that the rate of flow was increased 
significantly, but that the dead space of the vacuum chamber 22 created by 
contact of the tip 12 against the semiconductor wafer 14 did not achieve 
sufficient force for reliably securing the semiconductor wafer to the 
handling tool 10. It was also discovered that a serial connection of the 
pumps 40 and 42 by a hose 44 achieved the desired vacuum pressure. 
The flow path from the vacuum tip 12 to the pumps 40 and 42 includes a 
three-way valve 46. The valve 16 selectively links the tip 12 either to 
the pumps via a hose 48 or to the ambient atmosphere via a hose 50. 
Connection to the ambient atmosphere ensures an immediate release of even 
lightweight electronic workpieces, since no vacuum residue is allowed to 
remain in the dead space of the chamber 22 upon interruption of the path 
from the vacuum tip to the pumps. The position of a depressible button 52 
connected to a valve stem 54 determines the vacuum pressure at the chamber 
22. While the button 52 will be described as being connected to the valve 
stem 54, typically the button and valve stem are a single-piece structure. 
The method of manufacturing and/or attaching the button and valve stem are 
not critical. 
The three-way valve 46 is typically a normally open mechanism. That is, 
operating vacuum is available at the vacuum tip 12 unless valve stem 54 is 
depressed. One embodiment of such a valve is shown in FIG. 3, but other 
valving mechanisms are available. A coil spring 56 presses the valve stem 
54 into a raised position. In this position, an o-rinq 58 acts to seal a 
passageway 60 between a cap 62 and the valve stem. The passageway 60 leads 
to the ambient atmosphere, but the position of the o-ring prevents fluid 
communication between the ambient atmosphere and an inlet passageway 64 
leading to the vacuum tip. Instead, the inlet passageway to the vacuum tip 
is in fluid communication with an outlet passageway 66 to the pumps to 
create a vacuum pressure at the inlet passageway 64. Exerting pressure on 
the button 52 forces the valve stem 54 downwardly. Because the o-ring is 
mounted within a reduced-diameter portion 68 of the valve stem, the o-ring 
is moved from blocking engagement with the cap 62, allowing a free flow of 
air from the inlet passageway 64 to the passageway 60 to the ambient 
atmosphere. Full depression of the button lowers the o-ring into a sealing 
relationship with the body 16 to block airflow from the inlet passageway 
64 to the outlet passageway 66. 
While FIG. 2 illustrates the path to the ambient atmosphere as being 
through a hose 50, FIG. 3 shows that the passageway is actually along the 
valve stem 54. Consequently, unlike conventional prior art valving 
assemblies in which the valve stem slides along surrounding structure that 
is only slightly greater in diameter, here the valve stem is allowed to 
freely move in a manner that does not generate particulate contamination. 
In operation, the flow path from an inlet of the handling tool 10 to an 
outlet is from the vacuum tip 12 shown in FIG. 2 to the three-way valve 46 
and then to the serially connected pumps 40 and 42. The pumps are 
connected to a filter 70 by a hose 72 for use in a fabrication cleanroom 
environment. The filter 70 should be a submicron filter. From the filter 
70 the air is released into the ambient atmosphere by an outlet hose 74. 
Alternatively, the filter 70 may be mounted to the wall of the body 16 in 
order to eliminate the outlet hose 74. 
The body 16 is divided into two chambers 76 and 78 by a wall 80. The wall 
80 is not comparable to the division of the handling tool 10 into a base 
portion 82 and a handle portion 84 as shown in FIG. 1. Rather, the 
internal wall 80 provides an airtight isolation of the motors 36 and 38. 
Conventional motors include bushings that generate particles which would 
be detrimental to a fabrication cleanroom. An airtight isolation of the 
motors and the pumps 40 and 42 ensures that any generated particulate 
contamination remains within the body 16. Grommets 86 and 88 are utilized 
to allow passage of the hoses 48 and 72 through the internal wall 80. 
Preferably, grommets are also used for electrical lines that pass between 
the chambers 76 and 78. 
Particle generation is also retarded by exhausting the handling tool 10 
into the ambient atmosphere, as shown by outlet hose 74. An exhaust into 
the body 16 would disturb particles collected during the manufacture of a 
tool. 
A second embodiment of the present invention is shown in FIG. 4. The serial 
connection of two or more vacuum pumps is employed as described above, but 
rather than a stand-alone tool, the tool 90 of FIG. 4 includes a base 92 
connected to a wand handle 94 by a hose 96. The wand handle may be of any 
type known in the art. The wand handle includes a valve mechanism 97. 
Preferably, the valve mechanism is a three-way valve as described above. A 
vacuum tip 98 is identical to the one described above, having a vacuum 
chamber 100 and an inlet 102. A wand holder 104 is fixed to the base 92 
and positions the wand handle when not in use. 
The hose 96 is press fit to a fitting 106 that is the inlet to the base 92. 
The inlet connects to two or more serially connected vacuum pumps. A 
switch 108 is used to couple a battery pack to the vacuum pumps. A power 
lamp 116 illuminates when the pumps have been activated. An electrical 
jack 112 is used during recharging of battery pack. 
The two-piece tool of FIG. 4 may be used for applications in which an 
operator will remain in the same general area, while the stand-alone tool 
10 of FIG. 1 is more suited for applications in which an operator must 
move greater distances or must be concerned with ensuring that an 
attachment hose does not limit maneuverability. A third embodiment which 
is not shown would be one which secures an attachment to the base portion 
82 of FIG. 1 or the base 92 of FIG. 4 for coupling the base to a belt or 
the like of the operator, while the handle portion of the tool is held by 
the operator.