Texas Instruments | Evaluation of Nickel/Palladium/Gold-Finished Surface-Mount Integrated Circuits | Application notes | Texas Instruments Evaluation of Nickel/Palladium/Gold-Finished Surface-Mount Integrated Circuits Application notes

Texas Instruments Evaluation of Nickel/Palladium/Gold-Finished Surface-Mount Integrated Circuits Application notes
Application Report
SZZA026 – July 2001
Evaluation of Nickel/Palladium/Gold-Finished
Surface-Mount Integrated Circuits
Douglas Romm, Bernhard Lange, and Donald Abbott
Standard Linear & Logic
ABSTRACT
Texas Instruments has introduced a refined version of its nickel/palladium (NiPd) finish for
integrated circuit (IC) package leads. The enhanced version of lead finish is
nickel/palladium/gold (NiPdAu).
TI has a long and successful history with the NiPd finish. There are more than 40-billion
devices in the field with TI NiPd-finished leads. TI introduced the NiPd finish in 1989 and
many papers and studies have been published on it. With the push for Pb-free electronics,
TI decided to improve on the NiPd finish performance with Pb-free solders. The result is
the NiPdAu finish.
In September 2000, results were published for solderability tests on NiPd-finished
components using several Pb-free solder pastes that showed good performance. In that
work, preliminary data showed the excellent performance of NiPdAu component lead
finish with both a SnPbAg (control) solder and a SnAgCu (Pb-free) solder.
More extensive results are shown in this application report indicating good wetting
performance of the NiPdAu-finished ICs (dual-inline and quad package styles) with both
SnPbAg and SnAgCu solder alloys. Wetting balance tests showed quicker wetting time for
NiPdAu-finish component leads versus NiPd and SnPb component leads. Visual
inspection of solder joints made with NiPdAu-finished leads all gave acceptable wetting
performance, based on industry-standard criteria. Cross-sections of the solder joints
confirmed good wetting performance. Lead-pull test results were acceptable for all three
component finishes with both solder alloys and two different Pb-free printed wiring board
(PWB) finishes.
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Contents
Introduction .......................................................................................................................................... 4
Experiment ........................................................................................................................................... 5
Wetting Balance Test ..................................................................................................................... 6
Soldering Evaluations.......................................................................................................................... 8
PWB Coatings ................................................................................................................................ 8
Reflow Profiles ............................................................................................................................... 8
Test Equipment and Procedure .................................................................................................... 10
Performance Measures and Results............................................................................................. 10
Visual Appearance................................................................................................................ 10
Visual Appearance Results for Dual-Inline Packages ........................................................... 10
Visual Appearance Results for Quad Packages.................................................................... 12
Lead-Pull Test .............................................................................................................................. 13
Lead-Pull Data for Dual-Inline Packages ...................................................................................... 13
Lead-Pull Data for Quad Packages....................................................................................... 15
Solder-Joint Cross-Section Data................................................................................................... 19
Cross-Sections of Dual-Inline Packages ............................................................................... 19
Cross-Sections of Quad Packages ....................................................................................... 20
Cross-Sections Results......................................................................................................... 21
Results/Conclusions.......................................................................................................................... 22
Acknowledgment ............................................................................................................................... 22
References.......................................................................................................................................... 23
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Figures
Metal Stackup for TI Four-Layer NiPd Structure ........................................................................ 4
Metal Stackup for Three-Layer NiPdAu Finish ........................................................................... 4
Typical Wetting Balance Curve ................................................................................................... 6
Wetting Balance Curves for SnPb Component Finish With SnAgCu Solder ........................... 7
Wetting Balance Curves for TI NiPd Component Finish With SnAgCu Solder ........................ 7
Wetting Balance Curves for TI NiPdAu Component Finish With SnAgCu Solder.................... 7
Reflow Profile for SnPbAg Solder Alloy ..................................................................................... 9
Reflow Profile for SnAgCu Solder Alloy ..................................................................................... 9
NiPdAu Finish NS, SnPbAg Solder, NiAu PWB Finish............................................................. 10
SnPb Finish NS, SnPbAg Solder, NiAu PWB Finish ................................................................ 10
NiPdAu Finish NS, SnPbAg Solder, OSP PWB Finish ............................................................. 11
SnPb Finish NS, SnPbAg Solder, OSP PWB Finish ................................................................. 11
NiPdAu Finish NS, SnAgCu Solder, NiAu PWB Finish ............................................................ 11
SnPb Finish NS, SnAgCu Solder, NiAu PWB Finish ................................................................ 11
NiPdAu Finish NS, SnAgCu Solder, OSP PWB Finish ............................................................. 11
SnPb Finish NS, SnAgCu Solder, OSP PWB Finish................................................................. 11
NiPdAu Finish 176 PBL, SnPbAg Solder, NiAu PWB Finish ................................................... 12
NiPdAu Finish 176 PBL, SnAgCu Solder, NiAu PWB Finish ................................................... 12
NiPdAu Finish 176 PGF, SnPbAg Solder, NiAu PWB Finish ................................................... 12
NiPdAu Finish 176 PGF, SnAgCu Solder, NiAu PWB Finish ................................................... 12
NiPdAu Finish 208 PDV TQFP, SnPbAg Solder, NiAu PWB Finish ......................................... 13
NiPdAu Finish 208 PDV TQFP, SnAgCu Solder, NiAu PWB Finish......................................... 13
Evaluation of Nickel/Palladium/Gold-Finished Surface-Mount Integrated Circuits
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1
2
3
20 NS SOP Lead-Pull Results, OSP Pad Finish, Before and After Temperature Cycling ...... 14
20 NS SOP Lead-Pull Results, NiAu Pad Finish, Before and After Temperature Cycling...... 15
176 PBL TQFP Lead-Pull Results, OSP Pad Finish, Before and After Temperature Cycling 16
176 PBL TQFP Lead-Pull Results, NiAu Pad Finish, Before and After Temperature Cycling16
176 PGF TQFP Lead-Pull Results, OSP Pad Finish, Before and After Temperature Cycling 17
176 PGF TQFP Lead-Pull Results, NiAu Pad Finish, Before and After Temperature Cycling17
208 PDV TQFP Lead-Pull Results, OSP Finish, Before and After Temperature Cycling ....... 18
208 PDV TQFP Lead-Pull Results, NiAu Finish, Before and After Temperature Cycling....... 18
NiPdAu SOP, SnPbAg Solder, NiAu PWB Finish, 0 Temperature Cycles............................... 19
SnPb SOP, SnPbAg Solder, NiAu PWB Finish, 0 Temperature Cycles................................... 19
NiPdAu SOP, SnPbAg Solder, NiAu PWB Finish, 1000 Temperature Cycles ......................... 19
SnPb SOP, SnPbAg Solder, NiAu PWB Finish, 1000 Temperature Cycles............................. 19
NiPdAu SOP, SnAgCu Solder, NiAu PWB Finish, 0 Temperature Cycles............................... 20
SnPb SOP, SnAgCu Solder, NiAu PWB Finish, 0 Temperature Cycles .................................. 20
NiPdAu SOP, SnAgCu Solder, 1000 Temperature Cycles ....................................................... 20
SnPb SOP, SnAgCu Solder, 1000 Temperature Cycles ........................................................... 20
NiPdAu 208 PDV TQFP, SnPbAg Solder, NiAu PWB Finish, 0 Temperature Cycles.............. 21
SnPb 208 PDV TQFP, SnPbAg Solder, NiAu PWB Finish, 0 Temperature Cycles ................. 21
NiPdAu 208 PDV TQFP, SnAgCu Solder, NiAu PWB Finish, 0 Temperature Cycles.............. 21
SnPb 208 PDV TQFP, SnAgCu Solder, NiAu PWB Finish, 0 Temperature Cycles ................. 21
Tables
Solder Alloys Evaluated.............................................................................................................. 5
Components Used in Test .......................................................................................................... 5
Wetting Balance Data ................................................................................................................. 8
Evaluation of Nickel/Palladium/Gold-Finished Surface-Mount Integrated Circuits
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Introduction
A nickel/palladium (NiPd) finish for integrated circuit (IC) leads was first introduced in the late
1980s.[1,2] To date (July 2001), more than 40-billion NiPd-finished IC packages are in the field.
The four-layer NiPd structure is shown in Figure 1.
Palladium
Gold
Palladium
Nickel
Nickel
Palladium/Nickel Strike
Nickel Strike
Copper Base
Figure 1. Metal Stackup for TI
Four-Layer NiPd Structure
Copper Base
Figure 2. Metal Stackup for
Three-Layer NiPdAu Finish
In the early 1990s, a nickel/palladium/gold (NiPdAu) lead finish was introduced in the Japanese
market. This standardized three-layer NiPdAu finish is shown in Figure 2. Plating-layer
thicknesses for TI versions of both finish systems are available upon request.
Since its introduction, many Japanese IC users have opted to use the NiPdAu finish. A key
technical attribute of the NiPdAu finish is its enhanced wetting performance in solderability tests.
This has made the NiPdAu finish preferred in the Japanese market. Faster wetting times in
solderability tests may indicate improved wetting with the variety of Pb-free solder alloys
currently being evaluated by the electronics industry.
With the interest in Pb-free processing that developed through the mid-1990s, the need for
Pb-free package terminations became evident.[3,4,5,6,7,8,9] Because NiPd and NiPdAu are
Pb-free finishes, use of either on components, in conjunction with a Pb-free solder alloy and
organic solderability preservative (OSP) printed wiring board (PWB) pad finish, yields a Pb-free
solder joint. Two previous studies have been performed to evaluate a Pb-free solder joint formed
by using four-layer NiPd-finished IC components along with various Pb-free solder paste alloys
and an OSP PWB surface finish.[10,11] A limited number of NiPdAu-finished units also were
included in those previous studies for solder-wetting comparison.
Those studies showed that NiPd and NiPdAu finishes achieved equivalent, or better, lead-pull
and temperature-cycle results versus SnPb plated component leads (control). Any difference in
performance of the different lead finishes (SnPb, NiPd, NiPdAu) was merely visual.
The interest in use of the NiPdAu finish for component leads sparked its evaluation with the
industry-preferred Pb-free solder alloy, SnAgCu, which is presented here.
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Evaluation of Nickel/Palladium/Gold-Finished Surface-Mount Integrated Circuits
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Experiment
The Pb-free solder alloy chosen for this evaluation was 95.5Sn/3.9Ag/0.6Cu. This alloy has been
recommended by the National Electronics Manufacturing Initiative (NEMI) as a “standardized
Pb-free solder alternative.”[12] The decision was made to focus on performance of the NiPdAu
finish components with the SnAgCu solder alloy because this alloy is becoming the predominant
Pb-free paste being used.[13] The control paste chosen for comparison was 62Sn/36Pb/2Ag.
Melting point and peak reflow temperatures used for the two paste alloys are shown in Table 1.
Table 1.
Solder Alloys Evaluated
MELTING POINT
(°C)
PEAK
REFLOW USED
(°C)
62Sn/36Pb/2Ag
179
225
95.5Sn/3.9Ag/0.6Cu
217
235
ALLOY
For the SnAgCu alloy, NEMI has indicated that:
“use of the recommended alloys will raise the melting point by as much as forty
degrees, which obviously has an impact on a number of the materials and steps
in the assembly process, and affects companies throughout the supply chain.”[12]
Peak reflow temperature of 260°C has been mentioned as worst case across the industry for the
SnAgCu alloy. For this evaluation a peak reflow temperature of 235°C was chosen to
characterize performance of the SnAgCu alloy at a lower peak reflow temperature. Skidmore
reported that the best results were obtained using a linear profile at 235°C peak when evaluating
the solder alloy, flux chemistry, and profile.[14] Previous evaluations of SnAgCu solder alloy with
NiPd-finished components indicated no difference in wetting performance between units
soldered in a 235°C peak temperature and units soldered in a 260°C peak temperature.[11]
Test methods used in this evaluation included wetting balance, visual appearance examination,
lead-pull, and solder-joint cross-section. The various components used in these tests are shown
in Table 2.
Table 2.
Components Used in Test
PIN
COUNT
LEAD
PITCH
PACKAGE
DESIGNATOR
PACKAGE
STYLE
20
1.27 mm
NS
Dual inline
176
0.4 mm
PBL
Quad
176
0.5 mm
PGF
Quad
208
0.5 mm
PDV
Quad
Evaluation of Nickel/Palladium/Gold-Finished Surface-Mount Integrated Circuits
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Wetting Balance Test
The wetting balance (meniscograph) test can be used to test wettability of IC leads. However,
the wetting balance test is classified in ANSI/J-STD-002 as a “Test without established
Accept/Reject Criterion.”[15] This test method is recommended for engineering evaluations only,
not as a production pass/fail monitor.
The wetting balance test measures the forces imposed by the molten solder on the test
specimen as the specimen is dipped into and held in the solder bath. This wetting force is
measured as a function of time and is plotted. A typical wetting balance curve is shown in Figure
3. Initially, the force is negative, indicating that the solder has not yet begun to wet the specimen
and, in fact, shows a buoyancy effect. The force exerted by the solder approaches zero as the
solder begins to wet the specimen. One commonly used performance measure is the time to
cross the zero axis of wetting force, or t0. This point indicates the transition from nonwetting
(F < 0) to wetting (F > 0).
E quilib rated W etting F orce
Force
Z ero F orce L in e
B uo yancy A sso ciated W ith Initial No n-W etting
Time
Figure 3.
Typical Wetting Balance Curve
The wetting balance test was used to compare wetting performance of the three component lead
finishes used in this experiment. The NS (dual-inline) package style was used for wetting
balance tests. Samples of each component lead finish were tested and the wetting balance
curve for the combined readings was plotted. Figures 4 through 6 show the curves for SnPb,
NiPd, and NiPdAu, respectively. The three component lead finishes were tested with both SnPb
and SnAgCu solder globules.
The two evaluation criteria are time-to-zero, t0, and time to two-thirds maximum force, t2/3. t0 (as
described previously) is the transition point from nonwetting to wetting, indicated when the force
curve crosses the zero axis. Time to two-thirds maximum force is an arbitrary metric used to
compare total wetting time between samples.
Notice that the wetting balance curves for the NiPdAu-finish samples (Figure 6) show quicker
time to cross the zero axis and less variation in the maximum force when compared with SnPb
and NiPd component finishes. Similar results were seen when a SnPb solder globule was used.
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Evaluation of Nickel/Palladium/Gold-Finished Surface-Mount Integrated Circuits
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Figure 4.
Figure 5.
Wetting Balance Curves for SnPb Component Finish With SnAgCu Solder
Wetting Balance Curves for TI NiPd Component Finish With SnAgCu Solder
Figure 6.
Wetting Balance Curves for TI NiPdAu Component Finish
With SnAgCu Solder
Evaluation of Nickel/Palladium/Gold-Finished Surface-Mount Integrated Circuits
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A summary of the wetting balance data for the three component finishes, tested with both SnPb
(235°C) and SnAgCu (250°C) solders, is shown in Table 3.
Table 3.
Wetting Balance Data
SnPb GLOBULE
COMPONENT
FINISH
SnPb
t0
(s)
t2/3 MaxForce
(s)
0.41
1.16
NiPd
0.6
0.87
NiPdAu
0.31
0.61
SnAgCu GLOBULE
t0
(s)
t2/3 MaxForce
(s)
SnPb
0.41
0.79
NiPd
0.49
0.62
NiPdAu
0.33
0.57
COMPONENT
FINISH
The wetting balance data indicates that the NiPdAu finish wet faster (t0) than both the NiPd and
SnPb component finishes. Time to reach two-thirds maximum force also was faster for the
NiPdAu finish.
Soldering Evaluations
PWB Coatings
To evaluate Pb-free solder joints, two lead-free PWB coatings were used. The first was an OSP,
(ENTEK® PLUS CU-106A). This coating is a substituted benzimidazole that can preserve the
solderability of Cu through multiple soldering operations. The second pad coating used was a
NiAu finish. The specification for the Ni and Au layers was 5-µm to 7-µm Ni and 0.09-µm to
0.11-µm Au.
Reflow Profiles
Reflow profiles used were based on inputs from the solder-paste vendors. In our evaluation, the
reflow-profile temperatures were measured at the component lead. For the first run (SnPbAg
control), the profile shown in Figure 7 was used. This profile reaches a preheat temperature of
120°C to 160°C for approximately 60 seconds before rising to a peak temperature of 225°C to
228°C.
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Evaluation of Nickel/Palladium/Gold-Finished Surface-Mount Integrated Circuits
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Figure 7.
Reflow Profile for SnPbAg Solder Alloy
For the second run (SnAgCu alloy, 235°C peak), the profile shown in Figure 8 was used. This
profile reaches a preheat temperature of 120°C to 170°C for approximately 100 seconds before
rising to a peak temperature of 235°C to 238°C.
Figure 8.
Reflow Profile for SnAgCu Solder Alloy
Evaluation of Nickel/Palladium/Gold-Finished Surface-Mount Integrated Circuits
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SZZA026
Test Equipment and Procedure
The solder paste was printed using a 150-µm, polished, laser-cut stainless-steel stencil. An
optical alignment tool for manual component placement was used to align the device leads to the
solder paste prints. Optical inspection of the printed solder paste on the board was performed to
ensure adequate paste height and complete printing. For the reflow soldering process, a Rehm
full-convection reflow oven was used with nitrogen (N2) purge. Remaining oxygen (O2)
concentration was 500 ppm to 1000 ppm.
Performance Measures and Results
In this study, visual, mechanical, and reliability test methods were used to judge the performance
of the solder joints. The methods used and results obtained are presented in the following
paragraphs.
Visual Appearance
Solder-joint appearance was documented to identify the wetting performance of the
NiPdAu-finished components with both SnPbAg (control) and SnAgCu solder alloys. Samples
were judged against criteria in IPC-A-610C for general electronic products, dedicated service
electronic products, and high-performance electronic products.[16]
Visual Appearance Results for Dual-Inline Packages
Photographs of representative solder joints are shown in Figures 9 through 16 for the NS
package style. All solder joints exhibited a heel fillet height of at least 1× the lead thickness and
showed evidence of wetting to the sides of the leads. This performance would be considered
acceptable for all three classes of products identified in IPC-A-610C.[16]
Figure 9.
10
NiPdAu Finish NS, SnPbAg
Solder, NiAu PWB Finish
Figure 10. SnPb Finish NS, SnPbAg
Solder, NiAu PWB Finish
Evaluation of Nickel/Palladium/Gold-Finished Surface-Mount Integrated Circuits
SZZA026
Figure 11. NiPdAu Finish NS,
SnPbAg Solder, OSP PWB Finish
Figure 12. SnPb Finish NS, SnPbAg
Solder, OSP PWB Finish
Figure 13. NiPdAu Finish NS,
SnAgCu Solder, NiAu PWB Finish
Figure 14. SnPb Finish NS, SnAgCu
Solder, NiAu PWB Finish
Figure 15. NiPdAu Finish NS,
SnAgCu Solder, OSP PWB Finish
Figure 16. SnPb Finish NS, SnAgCu
Solder, OSP PWB Finish
Evaluation of Nickel/Palladium/Gold-Finished Surface-Mount Integrated Circuits
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SZZA026
Visual Appearance Results for Quad Packages
Photographs of representative solder joints are shown in Figures 17 through 22 for the quad
package styles. All solder joints exhibited a heel fillet height of at least 1× the lead thickness
and showed evidence of wetting to the sides of the leads. This performance would be
considered acceptable for all three classes of products identified in IPC-A-610C.[16]
Figure 17. NiPdAu Finish 176 PBL,
SnPbAg Solder, NiAu PWB Finish
Figure 19. NiPdAu Finish 176 PGF,
SnPbAg Solder, NiAu PWB Finish
12
Figure 18. NiPdAu Finish 176 PBL,
SnAgCu Solder, NiAu PWB Finish
Figure 20. NiPdAu Finish 176 PGF,
SnAgCu Solder, NiAu PWB Finish
Evaluation of Nickel/Palladium/Gold-Finished Surface-Mount Integrated Circuits
SZZA026
Figure 21. NiPdAu Finish 208 PDV TQFP,
SnPbAg Solder, NiAu PWB Finish
Figure 22. NiPdAu Finish 208 PDV TQFP,
SnAgCu Solder, NiAu PWB Finish
Lead-Pull Test
Lead-pull testing determined the force needed to pull an individual IC lead from the PWB land
pattern after soldering. First, to allow access to an individual lead on the PWB, all leads were cut
near the package body. Next, with the leads separated from the package body, the PWB was
fastened in a test fixture. Finally, the lead was pulled perpendicular to the PWB surface until it
separated from the PWB. The rate of movement of the test device was 0.4 mm/second vertically
to the board surface. The force needed to pull the lead from the PWB was measured and
recorded. Lead-pull data was taken before and after exposure to temperature cycling.
Lead-Pull Data for Dual-Inline Packages
Lead pull was performed on 20-pin SOP packages. Forty leads for each group were pulled to
obtain an average pull force. The unit of measure for pull force is newtons (N). Figures 23 and
24 indicate the average of lead-pull values for the NiPdAu, NiPd, and SnPb-finished packages
with SnPbAg and SnAgCu solder alloys. These data sets are for PWBs coated with OSP and
NiAu, respectively. Data points for the non-temperature cycled units are diamond shaped; data
points for the temperature cycled units are squares.
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Evaluation of Nickel/Palladium/Gold-Finished Surface-Mount Integrated Circuits
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40
35
Pull Force – N
30
25
20
15
10
5
SnPb
(SnAgCu)
NiPd
(SnAgCu)
NiPdAu
(SnAgCu)
SnPb
(SnPbAg)
NiPd
(SnPbAg)
NiPdAu
(SnPbAg)
0
Figure 23. 20 NS SOP Lead-Pull Results, OSP Pad Finish,
Before and After Temperature Cycling
The temperature-cycle excursion was −40°C to 125°C in 10-minute cycles. This was a
thermal-shock test, with the boards being moved from a −40°C chamber to a 125°C chamber.
There was no ramp between the temperature extremes.
For Figure 23(OSP PWB) and Figure 24 (NiAu PWB), essentially equivalent lead-pull results
were seen for each lead finish before and after temperature cycling. The minimum lead-pull
value specified by industry standards for non-temperature cycled samples (with the lead crosssectional area of the leads tested here) is 10 N [17,18]. Data points for the non-temperature
cycled units are diamond shaped; data points for the temperature cycled units are squares. All
lead-pull values were above this minimum requirement.
The SEMI standard states that: “the average lead-pull force of the temperature cycled units shall
be greater than half of the average lead pull force of the non-cycled units.”[17] The lead pull
values shown in Figure 23 and Figure 24 for temperature cycled units meet the industrystandard requirement.
14
Evaluation of Nickel/Palladium/Gold-Finished Surface-Mount Integrated Circuits
SZZA026
40
35
Pull Force – N
30
25
20
15
10
5
SnPb
(SnAgCu)
NiPd
(SnAgCu)
NiPdAu
(SnAgCu)
SnPb
(SnPbAg)
NiPd
(SnPbAg)
NiPdAu
(SnPbAg)
0
Figure 24. 20 NS SOP Lead-Pull Results, NiAu Pad Finish,
Before and After Temperature Cycling
Lead-Pull Data for Quad Packages
Lead pull was performed on the three quad package styles listed in Table 2. Forty leads for each
group were pulled to obtain an average pull force. For the three TQFP packages tested, the
minimum lead-pull value specified by the SEMI standard for non-temperature cycled samples
(based on the lead cross-sectional area of the units tested here) is 5 N.[17]
Figures 25 and 26 show the average of lead-pull values for the NiPdAu-, NiPd-, and SnPbfinished 176 PBL TQFP package with SnPbAg and SnAgCu solder alloys. These data sets are
for PWBs coated with OSP and NiAu, respectively.
Data points for the non-temperature cycled units are diamond shaped; data points for the
temperature cycled units are squares. This convention is followed throughout this section on
lead-pull results.
Evaluation of Nickel/Palladium/Gold-Finished Surface-Mount Integrated Circuits
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20
Pull Force – N
15
10
5
SnPb
(SnAgCu)
NiPd
(SnAgCu)
NiPdAu
(SnAgCu)
SnPb
(SnPbAg)
NiPd
(SnPbAg)
NiPdAu
(SnPbAg)
0
Figure 25. 176 PBL TQFP Lead-Pull Results, OSP Pad Finish,
Before and After Temperature Cycling
20
Pull Force – N
15
10
5
SnPb
(SnAgCu)
NiPd
(SnAgCu)
NiPdAu
(SnAgCu)
SnPb
(SnPbAg)
NiPd
(SnPbAg)
NiPdAu
(SnPbAg)
0
Figure 26. 176 PBL TQFP Lead-Pull Results, NiAu Pad Finish,
Before and After Temperature Cycling
Lead pull results for the 176 PBL TQFP packages showed essentially equivalent lead-pull values
for each lead finish before and after temperature cycling. All lead-pull values were above the
minimum requirement of 5 N for non-temperature cycled units.[17]
Figures 27 and 28 show the results for the 176 PGF TQFP package and Figures 29 and 30
show the lead pull results for the 208 PDV TQFP package on OSP- and NiAu-finished PWBs
with the solder pastes under evaluation. The results were similar to those seen in Figures 25 and
26 and the same conclusions can be drawn as to performance to the SEMI standard.
16
Evaluation of Nickel/Palladium/Gold-Finished Surface-Mount Integrated Circuits
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20
Pull Force – N
15
10
5
SnPb
(SnAgCu)
NiPd
(SnAgCu)
NiPdAu
(SnAgCu)
SnPb
(SnPbAg)
NiPd
(SnPbAg)
NiPdAu
(SnPbAg)
0
Figure 27. 176 PGF TQFP Lead-Pull Results, OSP Pad Finish,
Before and After Temperature Cycling
20
10
5
SnPb
(SnAgCu)
NiPd
(SnAgCu)
NiPdAu
(SnAgCu)
SnPb
(SnPbAg)
NiPd
(SnPbAg)
0
NiPdAu
(SnPbAg)
Pull Force – N
15
Figure 28. 176 PGF TQFP Lead-Pull Results, NiAu Pad Finish,
Before and After Temperature Cycling
Evaluation of Nickel/Palladium/Gold-Finished Surface-Mount Integrated Circuits
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20
Pull Force – N
15
10
5
SnPb
(SnAgCu)
NiPd
(SnAgCu)
NiPdAu
(SnAgCu)
SnPb
(SnPbAg)
NiPd
(SnPbAg)
NiPdAu
(SnPbAg)
0
Figure 29. 208 PDV TQFP Lead-Pull Results, OSP Finish,
Before and After Temperature Cycling
20
Pull Force – N
15
10
5
Figure 30. 208 PDV TQFP Lead-Pull Results, NiAu Finish,
Before and After Temperature Cycling
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Evaluation of Nickel/Palladium/Gold-Finished Surface-Mount Integrated Circuits
(SnAgCu)
SnPb
(SnAgCu)
NiPd
(SnAgCu)
NiPdAu
SnPb
(SnPbAg)
(SnPbAg)
NiPd
NiPdAu
(SnPbAg)
0
SZZA026
Solder-Joint Cross-Section Data
Cross-Sections of Dual-Inline Packages
Figures 31 through 38 show visual cross-section results for NS dual-inline packages, both before
and after exposure to 1000 temperature cycles of −40°C to 125°C. Cross-section results for the
dual-inline units verified good solder wetting performance that passes industry-standard
requirements.[16]
Figure 31. NiPdAu SOP, SnPbAg
Solder, NiAu PWB Finish,
0 Temperature Cycles
Figure 32. SnPb SOP, SnPbAg
Solder, NiAu PWB Finish,
0 Temperature Cycles
Figure 33. NiPdAu SOP, SnPbAg
Solder, NiAu PWB Finish,
1000 Temperature Cycles
Figure 34. SnPb SOP, SnPbAg
Solder, NiAu PWB Finish,
1000 Temperature Cycles
Evaluation of Nickel/Palladium/Gold-Finished Surface-Mount Integrated Circuits
19
SZZA026
Figure 35. NiPdAu SOP, SnAgCu
Solder, NiAu PWB Finish,
0 Temperature Cycles
Figure 36. SnPb SOP, SnAgCu
Solder, NiAu PWB Finish,
0 Temperature Cycles
Figure 37. NiPdAu SOP, SnAgCu
Solder, 1000 Temperature Cycles
Figure 38. SnPb SOP, SnAgCu
Solder, 1000 Temperature Cycles
Cross-Sections of Quad Packages
Figures 39 through 42 show visual cross-section results for TQFP packages prior to exposure to
temperature cycling. Cross-section results for quad packages verified good solder wetting
performance that passes industry-standard requirements.[16]
Evaluation of Nickel/Palladium/Gold-Finished Surface-Mount Integrated Circuits
20
SZZA026
Figure 39. NiPdAu 208 PDV TQFP,
SnPbAg Solder, NiAu PWB Finish,
0 Temperature Cycles
Figure 41. NiPdAu 208 PDV TQFP,
SnAgCu Solder, NiAu PWB Finish,
0 Temperature Cycles
Figure 40. SnPb 208 PDV TQFP,
SnPbAg Solder, NiAu PWB Finish,
0 Temperature Cycles
Figure 42. SnPb 208 PDV TQFP,
SnAgCu Solder, NiAu PWB Finish,
0 Temperature Cycles
Cross-Sections Results
All solder joints exhibited a heel fillet height at least 1× the lead thickness and showed evidence
of wetting to the sides of the leads. This performance is considered acceptable for all three
classes of products identified in IPC-A-610C.[16]
Evaluation of Nickel/Palladium/Gold-Finished Surface-Mount Integrated Circuits
21
SZZA026
Results/Conclusions
Wetting balance testing showed quicker wetting performance for the NiPdAu finish compared
with NiPd and SnPb component finishes. This result was seen with SnPbAg and SnAgCu solder
globules.
Visual appearance results and cross-section data indicate that an acceptable heel fillet of at
least 1× the lead thickness was achieved for all three component finishes with SnPbAg and
SnAgCu solder alloys.
Lead-pull results before and after temperature cycling were acceptable for all lead finishes when
compared to the criteria set out in industry standards.
The evaluation demonstrates that lead-free soldering is possible with currently used peak reflow
temperatures of 235°C to 240°C. Also, it was demonstrated that 260°C peak reflow temperature
is not mandatory for SnAgCu lead-free solder alloy when state-of-the-art, full-convection reflow
equipment is used.
Acknowledgment
The authors recognize the following employees of Texas Instruments for their professional
assistance: Kay Haulick and Martin Pauli for their board mount, visual documentation, and
lead-pull testing.
The authors recognize these solder-paste suppliers for support with materials and technical
information:
Alloy
SnPbAg
SnAgCu
Supplier
Multicore
Heraeus
Evaluation of Nickel/Palladium/Gold-Finished Surface-Mount Integrated Circuits
22
SZZA026.
References
1. D. C. Abbott, R. M. Brook, N. McLelland, and J. S. Wiley, IEEE Trans. CHMT, 14, 567
(1991).
2. A. Murata and D. C. Abbott, Technical Proceedings, Semicon Japan, 415 (1990).
3. M. Kurihara, M. Mori, T. Uno, T. Tani, and T. Morikawa, SEMI Packaging Seminar, Taiwan,
59 (1997).
4. I. Yanada, IPC Printed Circuits Expo 1998.
5. M. Jordan, Trans IMF, 75(4), 149 (1997).
6. T. Kondo, K. Obata, T. Takeuch, and Masaki, Plating and Surface Finishing, 51, February
1998.
7. R. Schetty, IPC Works 99 Proceedings, October 1999.
8. Y. Zhang, J. A. Abys, C. H. Chen, and T. Siegrist, SUR/FIN 96 (1996).
9. Ji-Cheng Yang, Kian-Chai Lee, and Ah-Chin Tan, Electronic Components and Technology
Conference Proceedings, 49th, 842-847 (1999).
10. D. W. Romm and D. C. Abbott, Lead Free Solder Joint Evaluation, Surface Mount
Technology, March 1998.
11. D. Romm, B. Lange, D. Abbott, Evaluation of Nickel/Palladium-Finished ICs With Lead-Free
Solder Alloys, Texas Instruments literature number SZZA024, January 2001.
12. NEMI Group Recommends Tin/Silver/Copper Alloy as Industry Standard for Lead-Free
Solder Reflow in Board Assemblies, NEMI press release, January 24, 2000.
13. IPC Roadmap, Third Draft (www.leadfree.org)
14. T. Skidmore and K. Walters, Circuit Assembly Magazine, April 2000.
15. IPC/EIA J-STD-002A, Solderability Tests for Component Leads, Terminations, Lugs,
Teminals, and Wires, October 1998.
16. IPC-A-610C, Acceptability of Electronic Assemblies, January 2000.
17. SEMI Draft Document #2910A, Test Method for the Solderability of Nickel/Palladium Lead
Finish on Surface Mount Semiconductor Devices, January 2001.
18. IEC 60068-2-21, Environmental Testing - PART 2-21: Robustness of Terminations and
Integral Mounting Devices (1999).
Evaluation of Nickel/Palladium/Gold-Finished Surface-Mount Integrated Circuits
23
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