IPC-4556 印制板化学镍钯浸金（ENEPIG）规范ENG - 第51页
IPC-4556-a6-1 Figure A6-1 Layout of T est Board Used for Solder Spread and Wetting Balance T esting Solder Spread Test Method The solder spread test pattern consists of 6 parallel traces, each 0.5 mm thick and 25 mm long…
APPENDIX 6
Solder Spread Testing
Brian Madsen
Continental Automotive Systems
Solder spread testing was performed on printed boards with seven different ENEPIG chemistries. Samples with a range of
electroless palladium thickness (targeted thicknesses from 0.1 to 0.5 µm) were provided for each of the seven chemistries.
While the intention had been to evaluate 3 to 4 electroless palladium thicknesses per chemistry through four test conditions,
unfortunately a shortage of samples for some chemistries resulted in incomplete data sets (see Table A6-S1). Two solder
pastes were used to evaluate the solder spread on the ENEPIG deposits - a Sn/Pb/Ag eutectic alloy solder paste with flux
activity level ROL1 and a SAC300 family Pb-free paste with flux activity level ROL0. For each solder paste, one test board
was subjected to 8 hours of damp heat conditioning at 72 °C [162 °F] and 85% relative humidity prior to printing the sol-
der paste, while a second board was printed with no pre-conditioning. Each individual test board contained 16 solder spread
coupons (layout shown in Figure A6-S1).
Table A6-S1 Preconditioning and Solder Paste Matrix Used for Solder Spread
Testing for a Given ENEPIG Chemistry and Electroless Palladium Thickness
(Note: When sufficient samples available)
None
8h 72° C/85%
None
8h 72° C/85%
0.1 µm X X X X
0.2 µm X X X X
0.3 µm X X X X
0.1 µm X X X X
0.2 µm X X X X
0.3 µm X X X X
0.1 µm X X
0.2 µm X X
0.3 µm X X
0.1 µm X X
0.2 µm X X
0.3 µm X X
0.1 µm X X
0.2 µm X X
0.3 µm X X
0.1 µm X X X X
0.2 µm X X X X
0.3 µm X X X X
0.5 µm X X X X
0.1 µm X X
0.2 µm X X
0.3 µm X X
0.5 µm X X
E
F
ENEPIG
G
Chemistry
Target Pd
Thickness
D
SnPb (ROL1) Pb-free (ROL0)
A
B
C
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IPC-4556-a6-1
Figure A6-1 Layout of Test Board Used for Solder Spread and Wetting Balance Testing
Solder Spread Test Method The solder spread test pattern consists of 6 parallel traces, each 0.5 mm thick and 25 mm long.
The key aspect of the spread test is the solder paste stencil design shown in Figure A6-2, which consists of 18 solder paste
deposits (0.5 mm x 0.5 mm) on each trace (108 total). The distance between the 18 paste deposits increases linearly across
the pattern, from a minimum of ~ 0.15 mm [6 mils] to a maximum of nearly 1 mm [38 mils].
SOLDERMASK DEFINED
SOLDERMASK CLEARANCE
SS-NN
MERIX
Figure A6-2 Solder Spread Pattern and Paste Stencil – Example of Solder Spread Pattern (left view) and Corresponding Solder Paste
Stencil Openings (right view)
January 2013 IPC-4556
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During reflow, solder deposits that contact each other tend to coalesce. Across the test pattern, the variation in the gaps
between paste deposits requires the solder to spread more at one end of the pattern for coalescence to occur. The overall
solder spread is calculated by first counting the number of distinct solder deposits remaining in each row of the pattern after
reflow. Then, the counts for the rows (‘‘x’’) are entered into the following equation:
108 −
φ=
Σ
i =l
6
x
i
z
102
100%
The result is a solder spread value expressed as a percent. A pattern exhibiting complete coalescence of the 18 deposits on
each row would achieve a sum of 6 (a count of 1 solder deposit per row x 6 rows), yielding a solder spread of 100%. If none
of the deposits coalesce, the sum is 108 and the solder spread is 0%, as expected. Figure A6-3 shows a solder spread result
of 14%.
ENEPIG Solder Spread Results:
SnPb Solder
The ROL1 Sn/Pb/Ag solder paste (using a SnPb solder profile) achieved very high solder spread percentages
(>90%) for all samples, regardless of ENEPIG chemistry, electroless palladium thickness, or pre-conditioning. There was no
meaningful differentiation between any of the samples (see Figures A6-4 and A6-5).
Figure A6-3 An Actual Solder Spread Result Showing the Deposits Counted for Each Line of the Pattern
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Line 1: 1234567891011121314 15 16
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