IPC-4556 印制板化学镍钯浸金（ENEPIG）规范ENG.pdf - 第52页
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 coalesce…
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)
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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
＝１６
＝１５
＝１６
＝１５
＝１６
＝１６
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Figure A6-4 Solder Spread Results Using an ROL1 Sn/Pb/Ag Solder Paste on ENEPIG Deposits
(Note: The ENEPIG deposits are from 7 different chemistry suppliers (with different electroless palladium thicknesses) using the solder spread
pattern. The Figure A6-4 - Top is for boards as-received. The Figure A6-4 - Bottom is for soldering after pre-conditioning of the boards for 8
hours at 72 °C [162 °F] and 85% RH).
110%
110%
110%
80%
70%
60%
50%
Solder Spread (%
0.00 0.05 0.10 0.15 0.20 0.25 0.300.35 0.40 0.45 0.50
)
SnPb ROL1 – No Conditionin
Actual Pd Thickness (um)
g
Chem A
Chem B
Chem C
Chem D
Chem E
Chem F
Chem G
110%
110%
110%
80%
70%
60%
50%
Solder Spread (%
0.00 0.05 0.10 0.15 0.20 0.25 0.300.35 0.40 0.45 0.50
)
Actual Pd Thickness (um)
SnPb ROL1 – Post 72 C/85% RH
Chem A
Chem B
Chem C
Chem D
Chem E
Chem F
Chem G
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