MIL-PRF-50884 Printed Wiring Board, Flexible Or Rigid-Flex, General Specification ForThis specification establishes the performance and qualification requirements for flexible and rigid-flex printed wiring boards with or without plated through holes \(see 6.1\). Verification is accomplished through the use of one of two methods of product assurance \(appendix A or appendix B\). Detail requirements, specific characteristics, and other provisions which are sensitive to the particular intended use are specified in the applicable master drawing.

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MIL�PRF�50884F

APPENDIX A

A.6.5 Certified suitable laboratories (acceptable to the Government). Government accepted test laboratories are

those facilities that have demonstrated their ability to perform the verification test required by this document. Levels

of acceptance include group A, group B, group C, and qualification testing.

A.6.6 Alternate test methods (see C.5.2.2). 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 appendix.

A.6.6.1 Flexibility endurance (see A.4.8.4.6). The flexibility endurance test may be performed using the alternate

test procedure detailed in test method number 2.4.3.1 of IPC�TM�650. The mandrel size for printed wiring board

types 1 and 2 shall be 12 times the sum of the total ply thickness reduced to the nearest .125 inch (3.18 mm). The

mandrel shall not be less than .125 inch (3.18 mm). The number of cycles until failure shall be reported.

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 revision D 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 annular

ring, internal annular ring, and other design criteria) 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 completed.

EXAMPLE: The master drawing of the most complex design selected for group B testing requires .003 inch

(0.08 mm) of copper plating thickness, .006 inch (0.15 mm) of dielectric spacing, and .005 inch (0.13 mm)

internal annular ring. These design details are considerably different than the baseline design parameters

found in either IPC�2223 or IPC�2221. If on these same samples, the group B test laboratory found that the

samples exhibited .002 inch (0.05 mm) of copper plating thickness, .005 inch (0.13 mm) of dielectric spacing

and .004 inch (0.10 mm) internal annular ring, the test laboratory could not claim, state, or certify that the

results of group B testing or the samples met the specification requirement.

A.6.8 Tin finishes (see A.3.4.1). 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 DLA Land and Maratime Form 19W. Copies of DLA Land and Maratime Form 19W, "PWB�QPL

Application/Authorization to Test" may be obtained at URL

Maritime, ATTN: VQE, P.O. Box 3990, Columbus, OH 43216�5000.

A.6.10 Alternate microsection preparation procedure guidelines. IPC�MS�810 "Guidelines for High Volume

Microsection" contains many recommendations and suggestions that can be helpful in preparing microsection mounts

containing multiple printed wiring board test specimens.

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.