MILPRF55110G
APPENDIX A
A.6.6
A.6.6 Alternate test methods. Other test methods may be substituted for those specified herein provided it is
demonstrated to and approved by the qualifying activity that such a substitution in no way relaxes the requirements of
this specification.
A.6.7
A.6.7 Group B sample critical design details. Past versions of this document contained default design details that
were assumed to apply to all test coupons subjected to group B inspection, regardless of the master drawing design
requirements. With the issuance of this document, the design details which were universally used to determine
acceptance or failure of the group B samples, are no longer considered universally applicable to the group B test
coupons. The printed wiring board design details (plating thickness, dielectric separation, external, and internal
annular ring, etc.) or the default design standard that applies to the test coupons, should be submitted along with test
coupons so that a proper group B evaluation of the design can be verified.
EXAMPLE: The master drawing of the most complex design selected for group B testing requires .0015
inch (0.038 mm) of copper plating thickness, .006 inch (0.15 mm) of dielectric spacing, and .003 inch
(0.076 mm) internal annular ring. These design details are considerably different than the baseline
design parameters found in IPC-2221. If on these same samples, the certified suitable laboratory found
that the samples exhibited .001 inch (0.025 mm) of copper plating thickness, .005 inch (0.13 mm) of
dielectric spacing and .002 inch (0.051 mm) internal annular ring, the manufacturer or certified suitable
laboratory could not claim, state, or certify that the results of group B testing or the samples met the
master drawing or specification requirements.
A.6.8
A.6.8 Tin finishes (see A.3.4.2). The use of alloys with tin content greater than 97 percent may exhibit tin whisker
growth problems after manufacture. Tin whiskers may occur anytime from a day to years after manufacture, and can
develop under typical operating conditions on products that use such materials. Tin whisker growth could adversely
affect the operation of electronic equipment systems. Conformal coatings applied over top of a whisker-prone surface
will not prevent the formation of tin whiskers. Alloys of 3 percent lead have shown to inhibit the growth of tin whiskers.
For additional information on this matter refer to ASTM B545.
A.6.9 DSCC Form 19W
A.6.9 DSCC Form 19W. Copies of DSCC Form 19W, "PWB-QPL Application/Authorization to Test" may be
obtained at https://www.dscc.dla.mil/offices/sourcing_and_qualification/ or upon application to DSCCVQE, PO Box
3990, Columbus, OH 43218-3990.
A.6.10
A.6.10 Alternate microsection preparation procedure guidelines. IPCMS810 "Guidelines for High Volume
Microsection" contains many recommendations and suggestions that can be helpful in preparing microsection mounts
containing multiple test specimens.
A.6.11
A.6.11 Microsection mount microetch caution. Prior to microetching, if lines are visible in the areas of inner layer
to hole wall interfaces, care should be taken to not over-etch the mount so that the various plating layers will still be
visible in the etched mount. This will enable accurate determination as to whether the line is separation or a polishing
artifact.
A.7
A.7. DEFINITIONS
A.7.1
A.7.1 Board thickness. The overall printed wiring board thickness includes metallic depositions, fusing, and solder
resist. The overall thickness is measured across the printed wiring board extremities (thickest part), unless a critical
area, such an edge-board contacts or card guide mounting location, is identified on the master drawing.
A.7.2
A.7.2 Complex (as related to group B testing). Complexity of printed wiring boards will usually depend on the base
materials used; dielectric layer thickness; overall printed wiring board thickness; number of conductor layers;
conductor widths and spacings; intricacy of patterns; size, quantity, aspect ratio and positioning of plated holes;
tolerancing of any or all of the above; the presence of internal heatsink planes or thermal planes, and all combinations
of the above with respect to their manufacturing difficulty, and their effects upon the consistent ability of the printed
wiring boards to meet the requirements of the periodic testing, unless otherwise specified by the contracting activity.
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