Applicable specifications do not adequately address requirements for PWB solderability.
The solderability of the PWB affects the quality of each solder joint since it is a significant part of the joint. Specifications do not clearly and consistently define solder coat thickness after fusing, and accelerated aging requirements, and solderability testing.
Since components and PWBs are joined by the soldering process, solderability and the test for solderability should be consistent.
(1) PWB solderability should meet MlL-P-55110. In addition, accelerated steam aging prior to testing should be performed in accordance with MIL-STD-883 method 2003.
(2) The following parameters should apply:
a. Solderability sample preparation: An AQL sample per applicable procurement document shall be exposed to 8.0 ± 0.5 hours of artificial steam aging per TM 2003 of MIL-STD-883C. Sample tem- perature during steam aging shall be maintained at a temperature range of 4șC to 10șC below the local boiling point of the water.
b. Type "R" flux: non-activated rosin, 25 to 35% solids content.
c. Solder temperature: 245 ± 5șC, solder bath composition Sn60 or Sn63, static bath.
d. Static Sn60 or Sn63 solder bath maintained to the following contamination limitations:
Elements Limits % Elements Limits %
- Copper 0.180
0.05 Arsenic 0.005
- Cadmium 0.005 Bismuth 0.25
0.003 Silver 0.01
- Aluminum 0.005 Nickel 0.01
Note: All Others--0.005%
(3) Product lots failing this solderability test should be returned to supplier.
5.4 Future Investigations
Recommended areas for investigations include:
(1) Objective methods of measuring solderability.
(2) Solder thickness required for consistent solderability.