AN90008

Recommendations for Printed Circuit Board assembly of
DSN0402B-2 (SOD992B)
Rev. 1.0 — 11 July 2019

application note

Document information
Information

Content

Keywords

DSN0402B-2, SOD992B, 01005 package size, reflow soldering, surface mount, solder paste,stencil aperture, PCB, SMD, footprint, landing pattern, pick and place, Chip Scale Package, CSP

Abstract

This application note provides guidelines for board assembly of the ultra-small DSN0402B-2(0.43 x 0.23 mm²) chip scale package. The main focus is on recommendations for reflow
soldering. For general information about footprint design and reflow soldering see application note
AN10365 (Surface mount reflow soldering description).

AN90008

Nexperia

Recommendations for Printed Circuit Board assembly of DSN0402B-2 (SOD992B)

1. Introduction
Due to the trend of reduced dimensions and increased density of functionality in smart phones
and other mobile devices, there is an increasing request from the industry for extremely
small components. With the new DSN0402B-2 (SOD992B) package which has a size of only
0.43 mm x 0.23 mm x 0.12 mm (01005), Nexperia offers an ultra-small surface mount chip scale
diode package to support this trend.
Due to the very small size of the component, Nexperia investigated the board assembly processintensively in order to offer board mounting recommendations.
This includes printed circuit board (PCB) mounting pads, stencil apertures, solder paste and board
assembly process parameters.
Using the recommended dimensions for pads and stencil as described in this document will help toachieve:•••••

optimum stand up heightminimum tilt
minimum rotation
good board assembly process performance
optimum board level reliability:
The reliability tests for qualification of the DSN0402B-2 device have been executed on PCBs
with the solder pads as recommended in this application note.

While this application note should help minimizing any unexpected failures, following the advice
in this document is not a guarantee for a perfect SMT assembly result. The results may differ
depending on the machine capability, ambient conditions, material, etc.

2. DSN0402B-2 (SOD992B) package details
The DSN0402B-2 (SOD992B) is a Discrete Silicon No Lead package (DSN). It features tin (Sn)plated metal contacts under the package (bottom terminations) similar to DFN style packages.
The DSN style package allows 100% utilization of the package area for active silicon, offeringa significant performance advantage per board area compared to products in plastic molded
packages.
The new production technology of the DSN0402B-2 results in very accurate dimensions. The
package comes with an extremely low overall height of 120 µm only.
Key features:
•
•
•
•
•
•
•

3

Ultra-small and flat package (0.43 x 0.23 x 0.12 mm )CSP package without side wall protection
The package area is 55% of the DSN0603 (SOD962)
Very low dimensional tolerances
Sn plated contacts for soldering on PCB
No package internal interconnects like wire bond or flip chipThis is beneficial to minimize impedance
Polarity marking visible from top and bottom (not applied for symmetric bi-directional diodes)
enables optical polarity check by pick and place machines and on PCB

While this application note should help minimizing any unexpected failures, following the advice
in this document is not a guarantee for a perfect SMT assembly result. The results may differ
depending on the machine capability, ambient conditions, material, etc.
The visual appearance is shown in Fig. 1. Fig. 2 shows the package dimensions.

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Recommendations for Printed Circuit Board assembly of DSN0402B-2 (SOD992B)

Remark: Bi-directional type without polarity indicator (notch)

AN90008

application noteFig. 1.

DSN0402B-2 (SOD992B) visual appearance

Fig. 2.

Package dimensions DSN0402B-2: Leadless ultra-small package; 2 terminals(SOD992B)

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Recommendations for Printed Circuit Board assembly of DSN0402B-2 (SOD992B)

3. PCB solder pattern
3.1. Solder pad design general options
There are two types of solder pad / solder resist designs:••

Solder Mask Defined (SMD)
Non-Solder Mask Defined (NSMD)

SMD is a method of designing the solder resist to partially overlap the Cu landing pattern on the
PCB, whereas NSMD designs have a gap between the solder resist and the Cu landing pattern on
the PCB. These two types are described in more detail in the next chapter.

3.1.1. Solder Mask Defined (SMD) pad versus Non-Solder Mask Defined(NSMD) pad
If the solder mask extends onto the solder lands, the remaining solderable area is solder mask
defined (SMD). The “effective” solder pad is equal to the copper area that is not covered by thesolder mask. This situation is illustrated in Fig 3a (left column). In case of a SMD pad, the copper
will normally extend 75 µm down to 50 µm underneath the solder mask on all sides. In other words,
the copper dimension is 0.1 mm to 0.15 mm larger than the solder mask dimension. These values
may vary depending on the class of PCBs used. This allows for tolerances in copper etching andsolder mask placement, during PCB production.
If the solder mask layer starts outside of the solder lands, and does not cover the copper, this isreferred to as NSMD. The “effective” solder pad is equal to the copper area. In case of a NSMD,
the solder mask should be at least 50 µm away from the solder land on all sides. In other words,
the solder mask dimension is 100 µm larger than the copper dimension. These values may varydepending on the class of PCBs used. The main requirement is that the solder mask is sufficiently
far away from the copper, such that – with the given tolerances in solder mask application – it does
not extend onto the copper. A NSMD footprint is shown in Fig 3b (right column).

001aac832

001aac831

a. Solder Mask Defined solder pads (SMD)
Fig. 3.

b. Non Solder Mask Defined solder pads (NSMD)

SMD versus NSMD solder pads

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Recommendations for Printed Circuit Board assembly of DSN0402B-2 (SOD992B)

3.2. Solder pad design for DSN0402B-2 (SOD992B)
3.2.1. Recommended reflow solder footprint
Based on the small dimensions of DSN0402B-2 (01005) devices and the given tolerances for PCB
manufacturing, it is recommended to use NSMD solder pads. Especially the gap between the Cu
pads (with the PCB design tolerances) is with 150 µm small for a reasonable solder resist trace.
In addition, such a resist trace would cause a higher tendency for tilting / rotation. Therefore, therecommended solder footprints are NSMD pads. Best soldering and reliability results have beenachieved if the PCB solder pad size is same as device pad size and electrical connection of thepads is realized by micro-vias. The solder footprints with dimensions are shown in Fig 4a. Fig 4bshows the solder footprints together with the package outline.

a. Reflow solder footprint
Fig. 4.

b. Reflow solder footprint and package outline

Recommended solder footprint for DSN0402B-2 (SOD992B)

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Recommendations for Printed Circuit Board assembly of DSN0402B-2 (SOD992B)

4. Solder stencil
4.1. Stencil recommendation
Due to small apertures and pad dimensions, a high-quality stencil should be used. E.g. for the
Nexperia investigations, a stainless-steel stencil, manufactured by laser-cut and with plasma
coating had been used. A nano-coated stencil has been investigated as well and is recommended
to achieve best release performance at solder paste printing..
For the recommended Nexperia footprint (see chapter 3.2.1, Fig. 4), the optimum stencil aperture2
is of size 0.2 x 0.13 mm . Based on stencil manufacturers’ experience, rounded corners with aradius of 0.065 mm will result in best solder paste release during printing and in an adequate solder
volume. For stencil apertures dimension, refer to Fig. 5.

Fig. 5.

Recommended stencil aperture

4.2. Stencil aperture design
Key design guidelines for stencil apertures are the area and aspect ratios. The area ratio for acommon approach should be >0.66. However, for ultra-small devices like DSN0402B-2, a smallerarea ratio needs to be applied to achieve optimum assembling reliability. Smaller values are
possible with adequate process control. Of course, it depends on the manufacturing environmentand other requirements of the manufacturer.
The aspect ratio should be >1.5 which is less critical to fulfil. For an explanation of area ratio andaspect ratio, refer to Fig 6.

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Recommendations for Printed Circuit Board assembly of DSN0402B-2 (SOD992B)

Fig. 6.

Explanation of area ratio and aspect ratio

Table 1. Area and aspect ratio for recommended stencil aperture
Stencil thickness T = 80 µm
Aperture size
Nexperia
recommended
footprint

2

200 x 130 µm

Area ratio

Aspect ratio

0.51

1.63

Table 2. Area and aspect ratio consideration for 100 µm stencil thickness
Stencil thickness T = 100 µm
Aperture size
Nexperia
recommended
footprint

2

200 x 130 µm

Area ratio

Aspect ratio

0.41

1.3

Table 1 shows the values for aspect and area ratio of the considered stencil apertures for a stencil
thickness of 80 µm. It results in an area ratio of 0.51 for the Nexperia footprint recommendation.
For such small area, the radius of the aperture (r = 65 µm) has been considered for the calculation.
In case of reduction to 75 µm stencil thickness, an area ratio of 0.54 with considering the 65 µm
radius can be achieved for the Nexperia recommended stencil aperture. For such small solder
footprint dimension an advanced process control is required.
In Table 2, the values for aspect and area ratio for a 100 µm thick stencil are listed. The minimal
footprints are surely not recommended any more for a 100 µm stencil thickness. The footprints
may work in a tightly controlled process (e.g. with help of 3D solder print inspection). In addition to
the stencil design guidelines, the potential device tilting also needs to be considered because of
relatively high solder paste volumes and variation in printing
Nexperia does not recommend to use a stencil thickness > 80 µm

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Recommendations for Printed Circuit Board assembly of DSN0402B-2 (SOD992B)

5. Solder paste
Besides stencil aperture and thickness, the solder paste used will have a significant impact on theprinting and soldering performance. Solder pastes are available in different solder powder grain
sizes. Refer to Table 3.
Table 3. Survey of solder paste types (grain sizes)
Type
Less than 0.5%,
10% max,
larger thanbetween

80% max,
between

10% max,
less than

1160

150 - 160

75 - 150

75

2

80

75 - 80

45 - 7545360

45 - 60

25 - 4525

450

38 - 50

20 - 3820

5

40

25 - 40

15 - 25156

25

15 - 25

5 - 155

7

15

11 - 15

2 - 11

2

Solder paste type 4.5 and 5 were used for investigations with Nexperia solder pad and stencil
aperture recommendation for the DSN0402B-2 (SOD992B) package with positive results. Using
type 4 solder paste tends to result in unstable solder volumes. For a reduction of the stencil
thickness to 60 µm it should be considered to use a type 6 solder paste.

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Recommendations for Printed Circuit Board assembly of DSN0402B-2 (SOD992B)

6. Soldering process
For soldering of DSN0402B-2 packages, the following solder processes were considered:•••

Convection reflow under nitrogen atmosphere is clearly preferred
Convection reflow under air atmosphere also works, but:
• Using an unfavorable layout results in DSN0402B-2 packages leaning towards undefinedplacement (tilting, rotating, misplacement) and in solder joints showing a tendency of
increased voiding• Solder joint surfaces are rough, flux residues often become darker and the soldering
behavior may deteriorate
Vapor phase soldering is also possible

For investigation of reflow soldering a profile as recommended for SAC alloys by IPC-7095 wasapplied. The heat-up slope should be limited to max 3 °C/s for such small devices. Refer to Fig. 7.
For reflow profile definition the recommendation of solder paste data sheet should be considered
as well.

Source IPC-7095C
Remark: Heat-up slope should be limited to max. 3 °C/s for DSN0402 devices
Fig. 7.

Reflow solder profile as applied for investigation

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Recommendations for Printed Circuit Board assembly of DSN0402B-2 (SOD992B)

7. Handling recommendations
Besides the PCB and stencil design requirements, the ultra-small size of the DSN0402B-2 andas consequence the low weight of the component requires that some attention be paid to the pick
and place (P&P) process. One effect which may cause problems during the pick and place (tapeout) process is electrostatic charge. Nexperia has implemented preventive measures such as
using a conductive plastic carrier tape (embossed tape) instead of a paper tape which is commonlyused for passive 01005 components. Of course, the cover tape is also static dissipative. Duringextensive P&P trials, however, it was observed that a relative humidity below 30% in the production
area leads to increased P&P (tape out) errors caused by electrostatic charging. Therefore, theenvironment should be controlled to >30% RH. In any case the feeders should be carefully
connected to ground to avoid electrostatic charging.
Another observation is that feeders of some P&P suppliers require inserts or springs below thecarrier tape. For embossed carrier tapes of such small components the inserts require a gap forthe carrier tape pockets to achieve a smooth indexing without vibration. In this case, P&P machine
suppliers should be contacted for recommendations.
It was found that it is beneficial for an optimum tape out yield if the cover tape peel off position is as
close as possible to the pick-up position of the devices. That prevents any rotation of products due
to mechanical movement and vibrations. A risk for rotation was still observed even the products
covered by a metal plate after cover tape peel off.
Manual handling by tweezers (e.g. for PCB repair) is strictly not recommended. This would damage
the package (CSP material is silicon).

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Recommendations for Printed Circuit Board assembly of DSN0402B-2 (SOD992B)

8. Summary
8.1. Recommended solder footprint and stencil aperture
The recommended solder footprint including stencil aperture is shown in Fig. 8.

Recommended stencil thickness: 80 µm
Fig. 8.

AN90008

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Solder footprint and stencil aperture

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Recommendations for Printed Circuit Board assembly of DSN0402B-2 (SOD992B)

8.1.1. Real device on recommended solder footprint

a. Side viewFig. 9.

b. Cross section

DSN0402B-2 soldered on recommended footprint, paste T5, stencil T = 80 µm

8.2. Further recommendations
8.2.1. Stencil layout and solder paste
•
•
•

•
•
•
•

Stencil thickness of 80 µm in combination with Type 5 or 4.5 solder paste (refer to Table 3) isrecommended
A no-clean paste with a J-STD-004 classification “L0” is recommended
Stencil thickness of 100 µm is clearly not recommended because:• The products tend to tilt due to the high amount of solder paste (see ”Diode-Tilting”)• The amount of printed solder paste tends to vary more compared to thinner stencils whichmakes the printing process unstable
A stencil aperture dimension as shown in Fig. 5 and Fig. 8 is recommended
The combination of solder paste and PCB solder pad surface finish needs to be evaluated toachieve an optimized solder paste print result
To get best printing (and soldering) results the cleaning cycle of the stencil should be wellcontrolled
A stainless-steel stencil, manufactured by laser-cut and with plasma coating should be used.
Further print performance improvement by use of a nano-coated stencil.

8.2.2. Solder pad design•••

AN90008

application note

NSMD pads with micro-via connection are recommended
Conductor (Cu trace) between solder pads on PCB is not recommended
Accuracy of PCB solder pad dimensions has significant impact on solder result. A tolerance ofat least ≤ 10% is recommended

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Recommendations for Printed Circuit Board assembly of DSN0402B-2 (SOD992B)

8.2.3. Soldering process
•
•

•
•

Convection reflow under nitrogen atmosphere is preferred
Convection reflow under air atmosphere also works, but:
• Using an unfavorable layout, products lean towards undefined tilting and rotation and solder
joints show a tendency of increased voiding• Solder joint surfaces are rough, flux residues often become darker and the soldering
behavior may deteriorate
For ultra-small devices with two terminals like DSN0402B-2 the convection airflow in the reflow
oven should be taken into account as it may cause tilting of devices.
Vapor phase soldering is also possible

8.2.4. Handling recommendations
•
•

•
•
•
•
•

Manual handling with tweezers (e.g. for repair) is not recommended
Feeders of P&P machines: if inserts are required underneath the carrier tape, a gap in thisinsert for the carrier tape pocket should be implemented.
Some feeders require a spring underneath the carrier tape.
The cover tape peel-off position should be as close as possible to the device pick-up position.
A reduction of feeding speed can help to improve tape out yield.
Ask P&P machine supplier for further recommendations.
Feeders should be carefully grounded to avoid electrostatic charging
Relative humidity for P&P should be >30%
The placement force of P&P machine should be 1N to 2N
Keep control of thawing time of solder paste bundle to avoid too much humidity in paste
Keep control of the time from solder paste printing until pick & place and reflow to avoid flux
drying

9. Revision history
Table 4. Revision history
Revision
Date
numberDescription

1.0

Initial version for DSN0402B-2, SOD992B

2019-07-11

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10. Legal information
Definitions
Draft — The document is a draft version only. The content is still underinternal review and subject to formal approval, which may result in
modifications or additions. Nexperia does not give any representations or
warranties as to the accuracy or completeness of information included hereinand shall have no liability for the consequences of use of such information.

Disclaimers
Limited warranty and liability — Information in this document is believed
to be accurate and reliable. However, Nexperia does not give any
representations or warranties, expressed or implied, as to the accuracy
or completeness of such information and shall have no liability for theconsequences of use of such information. Nexperia takes no responsibility
for the content in this document if provided by an information source outsideof Nexperia.
In no event shall Nexperia be liable for any indirect, incidental, punitive,
special or consequential damages (including - without limitation - lost
profits, lost savings, business interruption, costs related to the removalor replacement of any products or rework charges) whether or not suchdamages are based on tort (including negligence), warranty, breach ofcontract or any other legal theory.
Notwithstanding any damages that customer might incur for any reason
whatsoever, Nexperia’s aggregate and cumulative liability towards customer
for the products described herein shall be limited in accordance with theTerms and conditions of commercial sale of Nexperia.
Right to make changes — Nexperia reserves the right to make changes
to information published in this document, including without limitation
specifications and product descriptions, at any time and without notice. This
document supersedes and replaces all information supplied prior to the
publication hereof.
Suitability for use — Nexperia products are not designed, authorized or
warranted to be suitable for use in life support, life-critical or safety-criticalsystems or equipment, nor in applications where failure or malfunctionof an Nexperia product can reasonably be expected to result in personal
injury, death or severe property or environmental damage. Nexperia and its
suppliers accept no liability for inclusion and/or use of Nexperia products insuch equipment or applications and therefore such inclusion and/or use is at
the customer’s own risk.
Applications — Applications that are described herein for any of theseproducts are for illustrative purposes only. Nexperia makes no representation
or warranty that such applications will be suitable for the specified use
without further testing or modification.
Customers are responsible for the design and operation of their applications
and products using Nexperia products, and Nexperia accepts no liability forany assistance with applications or customer product design. It is customer’ssole responsibility to determine whether the Nexperia product is suitableand fit for the customer’s applications and products planned, as well as
for the planned application and use of customer’s third party customer(s).
Customers should provide appropriate design and operating safeguards tominimize the risks associated with their applications and products.
Nexperia does not accept any liability related to any default, damage, costs
or problem which is based on any weakness or default in the customer’s
applications or products, or the application or use by customer’s third party
customer(s). Customer is responsible for doing all necessary testing for thecustomer’s applications and products using Nexperia products in order toavoid a default of the applications and the products or of the application or
use by customer’s third party customer(s). Nexperia does not accept any
liability in this respect.
Export control — This document as well as the item(s) described herein
may be subject to export control regulations. Export might require a priorauthorization from competent authorities.
Translations — A non-English (translated) version of a document is forreference only. The English version shall prevail in case of any discrepancy
between the translated and English versions.

Trademarks
Notice: All referenced brands, product names, service names andtrademarks are the property of their respective owners.

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Recommendations for Printed Circuit Board assembly of DSN0402B-2 (SOD992B)

List of Tables
Table 1. Area and aspect ratio for recommended
stencil aperture.....................................................................7
Table 2. Area and aspect ratio consideration for 100µm stencil thickness.............................................................7
Table 3. Survey of solder paste types (grain sizes)............. 8
Table 4. Revision history....................................................13

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Recommendations for Printed Circuit Board assembly of DSN0402B-2 (SOD992B)

List of Figures
Fig. 1. DSN0402B-2 (SOD992B) visual appearance........... 3
Fig. 2. Package dimensions DSN0402B-2: Leadlessultra-small package; 2 terminals (SOD992B).......................3
Fig. 3. SMD versus NSMD solder pads............................... 4
Fig. 4. Recommended solder footprint for
DSN0402B-2 (SOD992B).................................................... 5
Fig. 5. Recommended stencil aperture................................ 6
Fig. 6. Explanation of area ratio and aspect ratio................ 7
Fig. 7. Reflow solder profile as applied for investigation...... 9
Fig. 8. Solder footprint and stencil aperture....................... 11
Fig. 9. DSN0402B-2 soldered on recommended
footprint, paste T5, stencil T = 80 µm................................12

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Recommendations for Printed Circuit Board assembly of DSN0402B-2 (SOD992B)

Contents
1. Introduction................................................................... 2
2. DSN0402B-2 (SOD992B) package details................... 2
3. PCB solder pattern.......................................................4
3.1. Solder pad design general options.............................. 4
3.1.1. Solder Mask Defined (SMD) pad versus NonSolder Mask Defined (NSMD) pad...................................... 4
3.2. Solder pad design for DSN0402B-2 (SOD992B)......... 5
3.2.1. Recommended reflow solder footprint...................... 5
4. Solder stencil................................................................ 6
4.1. Stencil recommendation.............................................. 6
4.2. Stencil aperture design................................................6
5. Solder paste.................................................................. 8
6. Soldering process........................................................ 9
7. Handling recommendations.......................................10
8. Summary..................................................................... 118.1. Recommended solder footprint and stencil aperture..118.1.1. Real device on recommended solder footprint........128.2. Further recommendations..........................................128.2.1. Stencil layout and solder paste...............................128.2.2. Solder pad design.................................................. 128.2.3. Soldering process................................................... 13
8.2.4. Handling recommendations.................................... 13
9. Revision history..........................................................13
10. Legal information......................................................14© Nexperia B.V. 2019. All rights reserved

For more information, please visit: http://www.nexperia.com
For sales office addresses, please send an email to: salesaddresses@nexperia.com
Date of release: 11 July 2019

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