AN90032

Low temperature soldering, application study
Rev. 1.1 — 22 February 2022

application note

Document information
Information

Content

Keywords

Low Temperature Soldering, LTS, SnBiX, board mounting, SMT, reflow

Abstract

This application note investigates SMT assembly using Low Temperature Solder (SnBiX) in reflowlines for Nexperia packages. Board mounting, thermal and mechanical behavior are analyzed. All
Nexperia packages can be soldered using SnBiX solder pastes.

AN90032

Nexperia

Low temperature soldering, application study

1. Introduction
New generation Low Temperature Solder (LTS) pastes for Surface Mount Technology (SMT) is
proposed for low temperature applications such as computing. LTS pastes are commonly build
on near-eutectic SnBi alloying system and therefore show reduced melting temperatures which
reduces the reflow temperatures as well as the energy consumption during SMT by up to 40%.
This translates into reduced CO2 emissions and reduced manufacturing cost. Additionally, such
effect can improve the yield impact created by high temperature (HT) warpage. HT warpage is
widely recognized seen as main driver to reduce the reflow temperature for SMT. New productmarkets such as ultra-mobile computing and the Internet of Things (IoT) drive the need for smaller
and thinner packages and boards which can suffer warpage by reflow temperatures of current
solder systems like SAC. By lowering the peak temperature during reflow, warpage is reduced,
resulting in higher SMT yields.
To safeguard the usage of Nexperia products on LTS assembly lines an internal investigation was
carried out proving LTS readiness of Nexperia's package families. This application note will givedetails on the analysis and guideline for possible use of LTS solder.
Since Nexperia's package portfolio consists of various lead finish technologies, family
representatives of these technologies were selected and mounted on a printed-circuit board (PCB)
using standard SAC and new LTS solder.

2. LTS application study
To safeguard potential application of Nexperia products in LTS assembly lines, a range of
packages were validated compared to standard SAC solder. By that valuable insights of LTS
assembly were gained and will be shared.
Six representative packages were subjected to the following test plan:•••

AN90032

application note

0 hour characterization:• Ceramic plate test
• Microsection• Optical inspection• X-ray inspection
Board level Reliability• Thermal cycling• Drop testing
Mechanical testing• Shear testingAll information provided in this document is subject to legal disclaimers.

Rev. 1.1 — 22 February 2022

© Nexperia B.V. 2022. All rights reserved

2 / 21

AN90032

Nexperia

Low temperature soldering, application study

3. Set up and Materials
3.1. Package selection
Various packages have been chosen to cover Nexperia's plating and leadframe technologies.
Fig. 1 shows the selection. Six products were used in this application study.

Fig. 1.

Package selection
This selection covers:
•
•
•
•
•

SOT363: NiFe leadframe + Cu plating and Sn finish
DFN1010B-6 (SOT1216), DFN1110D-3 (SOT8015) Cu leadframe with NiPdAu plating and Sn
finishLFPAK56 (SOT669): Cu leadframe with Sn finish
WLCSP12: WLCSP with SAC solder balls
DSN0603-2 (SOD962): DSN with CuSn pads

3.2. Footprint and stencil design
Footprint and stencil design were chosen according to product recommendations for the selected
packages, see Fig. 1.
As PCB material, 8 layer FR4 boards according to JESD22-B111/A104 were used. WLCSP12 andDFN1110D-3 were assembled on drop test PCB layout while the other packages were soldered onreliability boards. The footprints used are shown in Fig. 2, (see also Appendix 1) and examples of
PCBs in Fig. 3.

AN90032

application note

All information provided in this document is subject to legal disclaimers.

Rev. 1.1 — 22 February 2022

© Nexperia B.V. 2022. All rights reserved

3 / 21

AN90032

Nexperia

Low temperature soldering, application study

DFN1110D-3

DFN1010B-6

SOT363

DSN0603
0.85
0.6
0.2

0.2

0.2

0.4

0.4 0.28

0.256

LFPAK56

Fig. 2.

0.16

0.256

WLCSP12

Examples of footprints used

AN90032

application note

All information provided in this document is subject to legal disclaimers.

Rev. 1.1 — 22 February 2022

© Nexperia B.V. 2022. All rights reserved

4 / 21

AN90032

Nexperia

Low temperature soldering, application study

drop test PCB (DFN1110D-3)
Fig. 3.

reliability test PCB (LFPAK56)

Examples of drop test PCB and reliability PCB

3.3. Solder paste
As Low Temperature Solder paste, a commercially available, near eutectic SnBiX alloy(Sn42Bi57.6Ag0.4) Type 5 was used. As comparison, trails were conducted using SAC305 Type
4.5 alloy. Further paste printing details are shown in Table 1.

AN90032

application note

Table 1. Solder paste printing details
PackageStencil thickness [µm]Print speed [mm/s] Squeegee force [N]DSN0603

80

40

45

DFN1010-6

100

35

49

DFN1110D-3

100

35

55

SOT363

100

35

49

LFPAK56

120

35

49

WLCSP12

80

40

45

All information provided in this document is subject to legal disclaimers.

Rev. 1.1 — 22 February 2022

© Nexperia B.V. 2022. All rights reserved

5 / 21

AN90032

Nexperia

Low temperature soldering, application study

4. Reflow profile
Reflow profile should be adjusted according to the data sheet of the solder material supplier.
Soldering was done under nitrogen atmosphere.
Fig. 4 shows the profile of SnBiX solder compared to SAC solder used in the application study.
aaa-034489

300

peak
temperature
SAC: 240 °C

Ts
(°C)
200

LTS: 190 °C

SAC
LTS

100

0
0

Fig. 4.

100

200

300

time (s)400

Reflow profile for LTS and SAC solder pastes

5. Results
5.1. 0 hour characterization
5.1.1. Ceramic plate test
In the ceramic plate test, solder paste is printed onto a ceramic substrate, followed by package
placement and reflow. Further, the reflowed solder on the leads of the package is visually inspected
to determine the wetting characteristics.
••

Fig. 5.

Wetting performance of all packages are according to requirements (>95%)
No difference in wetting performance between LTS and SAC

Wetting performance

AN90032

application note

All information provided in this document is subject to legal disclaimers.

Rev. 1.1 — 22 February 2022

© Nexperia B.V. 2022. All rights reserved

6 / 21

AN90032

Nexperia

Low temperature soldering, application study

5.1.2. Optical inspection
No significant differences between LTS and SAC solder paste except for slightly higher solder
paste volume when using LTS solder have been observed. Better release performance of LTS
solder paste is suspected because of different flux system.

Fig. 6.

PCB after solder paste printing and placement

AN90032

application note

All information provided in this document is subject to legal disclaimers.

Rev. 1.1 — 22 February 2022

© Nexperia B.V. 2022. All rights reserved

7 / 21

AN90032

Nexperia

Low temperature soldering, application study

5.1.3. Microsection
Microsection images of all packages confirms good wettability of LTS and SAC solder. Both alloys
show homogeneous inter-metallic compounds (IMC). For SnBiX alloy, lamellar Bi-Sn microstructureis visible. WLCSP12 forms hybrid joint to SAC solder ball while the solder ball does not collapse
during reflow.

Fig. 7.

Microsections of LTS and SAC solder joints after reflow

5.1.4. X-ray inspection
X-ray inspection to cross check the wetting performance and solder voids. No significant difference
between LTS and SAC solder is visible in X-ray.

Fig. 8.

X-ray inspection after reflow

AN90032

application note

All information provided in this document is subject to legal disclaimers.

Rev. 1.1 — 22 February 2022

© Nexperia B.V. 2022. All rights reserved

8 / 21

AN90032

Nexperia

Low temperature soldering, application study

5.2. Board level reliability
5.2.1. Thermal cycling
Temperature cycling test was executed (TCT / JESD22-A104D) according to condition N and G for
LTS soldered samples, see Table 2. Electrical testing after soldering on PCB and after TCT wasdone with the standard tests per type. For DFN1110D-3 and WLCSP12 daisy chain samples within-situ resistance monitoring in TCT were used.
No solder related differences could be detected between devices soldered with SAC and LTS. For
LTS solder joints, grain coarsening was observed after 1500 cycles as shown in Fig. 9.
Table 2. TCT conditions according to JESD22-A104D
Test condition
Nominal Ts(min) with tolerances

Nominal Ts(max) with tolerancesA-55 (+0,-10)+85 (+10,-0)

B-55 (+0,-10)+125 (+15,-0)C-65 (+0,-10)+150 (+15,-0)G-40 (+0,-10)+125 (+15,-0)

H-55 (+0,-10)+150 (+15,-0)I-40 (+0,-10)+155 (+15,-0)J-0 (+0,-10)+100 (+15,-0)K-0 (+0,-10)+125 (+15,-0)

L-55 (+0,-10)+110 (+15,-0)M-40 (+0,-10)+150 (+10-0)N-40 (+0,-10)+85 (+10,-0)

In addition to required testing condition N for computing applications, TCT condition G has also
been passed on all tested products soldered with LTS. Samples soldered with SAC solder paste
were tested as a direct reference.
Table 3. TCT results for condition N and G
Numberof
DSN0603-2
DFN1010B-6
cycles
LTS
SAC
LTS
SAC

Number of failures / total
SOT363

LFPAK56

DFN1110D-3

WLCSP12

LTS

SAC

LTS

SAC

LTS

SAC

LTS

SAC

0

0/80

0/80

0/75

0/80

0/80

0/80

0/80

0/80

0/60

0/60

0/48

0/48

500

0/80

0/80

0/75

0/80

0/80

0/80

0/80

0/80

0/60

0/60

0/48

0/48

750

0/80

0/80

0/75

0/80

0/80

0/80

0/80

0/80

0/60

0/60

0/48

0/48

1000

0/80

0/80

0/75

0/80

0/80

0/80

0/80

0/80

0/60

0/60

0/48

0/48

1250

0/80

0/80

0/75

0/80

0/80

0/80

0/80

0/80

0/60

0/60

0/48

0/48

1500

0/80

0/80

0/75

0/80

0/80

0/80

0/80

0/80

0/60

0/60

0/48

0/48

AN90032

application note

All information provided in this document is subject to legal disclaimers.

Rev. 1.1 — 22 February 2022

© Nexperia B.V. 2022. All rights reserved

9 / 21

AN90032

Nexperia

Low temperature soldering, application study

Fig. 9.

Microsection after 1500 cycles, exemplary for condition N

5.2.2. Drop testing
Two packages were tested, WLCSP (hybrid solder joint) and DFN1110D-3. Both packages were
tested according to JEDEC specification (JESD22-B111) and drop test was performed for samples
soldered with SAC and LTS solder paste.
Both packages passed the JEDEC requirements (>100 drops) and withstood >2000 drops with nooccurrence.

6. Mechanical testing
6.1. Shear testing
Package shear strength was determined at 0 hour condition and after 1500 cycles TCT (condition
N). Shear strength at 0 hour is found slightly higher for LTS solder compared to SAC solder joints
as expected from higher mechanical strength of LTS solder reported in data sheet. All solder joints
show acceptable shear strength degradation after 1500 cycles, compare Table 4.
All packages fulfill industry established requirements.
Table 4. Shear testing results
Package
Shear strength [N]
0 cycles1500 cycles

LTS

SAC

LTS

SAC

DSN0603

5.88 ± 0.20

5.49 ± 0.20

4.81 ± 0.29

4.90 ± 0.78

DFN1010-6

13.14 ± 0.69

12.26 ± 0.78

12.94 ± 1.57

11.08 ± 0.59

DFN1110D-3

28.64 ± 4.51

24.61 ± 3.43

27.36 ± 3.53

22.95 ± 2.16

WLCSP1211.38 ± 0.69

12.26 ± 0.59

12.26 ± 0.20

11.77 ± 0.49

SOT36317.46 ± 1.57

11.57 ± 0.20

14.51 ± 0.69

11.28 ± 0.10

LFPAK56

339.41 ± 32.56

265.56 ± 49.62

324.21 ± 33.24

278.12 ± 18.93

AN90032

application note

All information provided in this document is subject to legal disclaimers.

Rev. 1.1 — 22 February 2022

© Nexperia B.V. 2022. All rights reserved

10 / 21

AN90032

Nexperia

Low temperature soldering, application study

7. Conclusion
An extensive application study has been run on LTS assembly covering all Nexperias package
platforms. Paste printing, wettability and product placement have shown comparable performance
to SAC solder assembly.
After careful adjustment to LTS reflow profile, the reflow process can be run analogue to known
procedures. LTS solder joints proved comparable performance, reliability has been proven byboard level reliability (thermal cycling), drop test performance and joint strength in comparison to
SAC solder joint.
Lower overall energy input and peak temperatures during reflow will reduce system warpage andenergy consumption.
Thermal cycling was tested up to 125 °C (condition G), however customers are responsible inwhich application LTS will be applied.
All Nexperia packages can be soldered with no special precautions using SnBiX solder
pastes.

8. Further remarks
Stencil design
For small solder pads an optimization of stencil apertures individual per solder paste isrecommended. It was found that underlying flux systems can lead to changes in release properties
in stencil printing process.

Electromigration
Electromigration was not observed in this study. Care should be taken for high current transmitting
packages.

Units
If not otherwise stated, all measurement units given in this document are metric units. This meansthat also the package nomenclature, i.e. the term “0603”, refers to metric units.

9. Revision history
Table 5. Revision history
Revision
Date
numberDescription

1.1

2022-02-22

DSN0603 footprint drawing updated in Fig. 2.

1.02022-02-18

Initial version.

AN90032

application note

All information provided in this document is subject to legal disclaimers.

Rev. 1.1 — 22 February 2022

© Nexperia B.V. 2022. All rights reserved

11 / 21

AN90032

Nexperia

Low temperature soldering, application study

10. Appendix 1: reflow soldering footprints
DFN1110D-3

Footprint information for reflow soldering of DFN1110D-3 package

SOT8015

1.4
0.45

0.2

0.35

0.3

0.25
0.65

0.6

0.5

0.4

0.12 0.22
1.8
0.34 0.44
0.88 0.78 0.68
0.34

0.34

0.2
0.3
0.4
0.8

occupied area

solder resist

solder lands

solder paste

0.9
1.0
recommended stencil thickness: 0.1 mm

Dimensions in mm
Issue date

19-11-27

AN90032

application note

sot8015_fr

All information provided in this document is subject to legal disclaimers.

Rev. 1.1 — 22 February 2022

© Nexperia B.V. 2022. All rights reserved

12 / 21

AN90032

Nexperia

Low temperature soldering, application study
DFN1010B-6

Footprint information for reflow soldering of DFN1010B-6 package

SOT1216

0.9
0.35

0.35

0.15 0.2 (6x) 0.15

1.3

1.2

0.35

0.25

0.5

0.6

0.35

0.25

1.1

0.3 (6x)1
1.35

solder paste

solder land plus solder paste

occupied area

solder resist

Dimensions in mm
Issue date

14-07-28
17-03-31

AN90032

application note

sot1216_fr

All information provided in this document is subject to legal disclaimers.

Rev. 1.1 — 22 February 2022

© Nexperia B.V. 2022. All rights reserved

13 / 21

AN90032

Nexperia

Low temperature soldering, application study
2.65

SOT363solder lands
2.35 1.5

0.4 (2×)

0.6 0.5(4×) (4×)

solder resist
solder paste

0.5
(4×)

0.6
(2×)

0.6
(4×)

Dimensions in mm
1.8

AN90032

application note

occupied area

All information provided in this document is subject to legal disclaimers.

Rev. 1.1 — 22 February 2022

sot363_fr© Nexperia B.V. 2022. All rights reserved

14 / 21

AN90032

Nexperia

Low temperature soldering, application study
DSN0603

Footprint information for reflow soldering of leadless ultra small package; 2 terminals

SOD962

0.85
0.6
0.2

0.2

0.2

0.4

0.4 0.28

0.256

0.16

0.256

recommended stencil thickness: 0.1 mm

occupied area

solder paste

solder lands
Dimensions in mm
Issue date

16-01-26
20-09-15

AN90032

application note

sod962_fr

All information provided in this document is subject to legal disclaimers.

Rev. 1.1 — 22 February 2022

© Nexperia B.V. 2022. All rights reserved

15 / 21

AN90032

Nexperia

Low temperature soldering, application study
LFPAK56
4.7
4.2

0.25
(2×)

0.9
(3×)

0.25
(2×)

0.6
(4×)

3.45
0.6
(3×)

2

3.5

2.55

0.25
(2×)
SR opening =Cu + 0.075

1.1
2.15
3.3

SP opening =Cu - 0.050

0.7
(4×)

1.27
3.81

AN90032

application note

solder lands

solder paste
125 µm stencil

solder resist

occupied area

All information provided in this document is subject to legal disclaimers.

Rev. 1.1 — 22 February 2022

sot1023_fr© Nexperia B.V. 2022. All rights reserved

16 / 21

AN90032

Nexperia

Low temperature soldering, application study
WLCSP12
1.65
0.5

2.15

0.5

0.5

0.2

0.23

0.27

0.5

Recommended stencil thickness: 0.08mm
REFLOW SOLDERING

AN90032

application note

Occupied Area

Solder Resist

Solder Land

Solder Paste

All information provided in this document is subject to legal disclaimers.

Rev. 1.1 — 22 February 2022

© Nexperia B.V. 2022. All rights reserved

17 / 21

AN90032

Nexperia

Low temperature soldering, application study

11. 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.

AN90032

application note

All information provided in this document is subject to legal disclaimers.

Rev. 1.1 — 22 February 2022

© Nexperia B.V. 2022. All rights reserved

18 / 21

AN90032

Nexperia

Low temperature soldering, application study

List of Tables
Table 1. Solder paste printing details...................................5
Table 2. TCT conditions according to JESD22-A104D.........9
Table 3. TCT results for condition N and G......................... 9
Table 4. Shear testing results............................................ 10
Table 5. Revision history....................................................11

AN90032

application note

All information provided in this document is subject to legal disclaimers.

Rev. 1.1 — 22 February 2022

© Nexperia B.V. 2022. All rights reserved

19 / 21

AN90032

Nexperia

Low temperature soldering, application study

List of Figures
Fig. 1. Package selection.....................................................3
Fig. 2. Examples of footprints used..................................... 4
Fig. 3. Examples of drop test PCB and reliability PCB.........5
Fig. 4. Reflow profile for LTS and SAC solder pastes.......... 6
Fig. 5. Wetting performance.................................................6
Fig. 6. PCB after solder paste printing and placement.........7
Fig. 7. Microsections of LTS and SAC solder joints
after reflow........................................................................... 8
Fig. 8. X-ray inspection after reflow..................................... 8
Fig. 9. Microsection after 1500 cycles, exemplary forcondition N......................................................................... 10

AN90032

application note

All information provided in this document is subject to legal disclaimers.

Rev. 1.1 — 22 February 2022

© Nexperia B.V. 2022. All rights reserved

20 / 21

AN90032

Nexperia

Low temperature soldering, application study

Contents
1. Introduction................................................................... 2
2. LTS application study.................................................. 2
3. Set up and Materials.................................................... 3
3.1. Package selection....................................................... 3
3.2. Footprint and stencil design........................................ 3
3.3. Solder paste................................................................ 5
4. Reflow profile................................................................6
5. Results...........................................................................6
5.1. 0 hour characterization................................................ 6
5.1.1. Ceramic plate test.................................................... 6
5.1.2. Optical inspection..................................................... 7
5.1.3. Microsection..............................................................8
5.1.4. X-ray inspection........................................................ 8
5.2. Board level reliability................................................... 9
5.2.1. Thermal cycling........................................................ 9
5.2.2. Drop testing............................................................ 10
6. Mechanical testing......................................................10
6.1. Shear testing............................................................. 10
7. Conclusion.................................................................. 11
8. Further remarks.......................................................... 11
9. Revision history..........................................................11
10. Appendix 1: reflow soldering footprints................. 12
11. Legal information......................................................18© Nexperia B.V. 2022. 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: 22 February 2022

AN90032

application note

All information provided in this document is subject to legal disclaimers.

Rev. 1.1 — 22 February 2022

© Nexperia B.V. 2022. All rights reserved

21 / 21