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.3.5.5.3 Discoloration. Discoloration of metallic surfaces under the cured solder mask is acceptable.

A.3.5.5.4 Registration (see figures F�11 and F�12). The solder mask shall be registered to the land or terminal

patterns in such a manner as to meet the requirements specified (see A.3.1.1). If no requirements are specified, the

following apply:

For plated-through holes and vias, the following shall apply:

(1)

Solder mask misregistration onto plated-through component hole lands (plated-through holes to which

solder connections are to be made) shall not reduce the external annular ring below the specified

minimum requirements.

(2)

Solder mask shall not encroach into plated-through hole barrels or onto other surface features (such

as edge board contacts, or lands of unsupported holes) to which solder connections will be made.

(3)

Solder mask is permitted in plated holes or vias in which no lead is to be soldered.

For surface mount lands with no plated-through holes, the following shall apply:

(1)

For lands with a pitch of .050 inch (1.27 mm) or greater, solder mask encroachment is on one side of

land only and does not exceed .002 inch (0.050 mm).

(2)

For lands with a pitch less than .050 inch (1.27 mm), solder mask encroachment is on one side of land

only and does not exceed .001 inch (0.025 mm).

For ball grid array lands, the following shall apply:

(1)

If the land is solder mask defined, allowable misregistration of the solder mask causes breakout of the

land of not more than 90 degrees.

(2)

If the land is copper defined, the solder mask shall not encroach onto the land. Solder mask on the

land-to-via connecting conductor shall be acceptable.

(3)

If solder mask dam is specified, the dam remains in place with the conductor to the via covered.

Edge-board contacts and test points which are intended for assembly testing shall be free of solder mask

unless a partial coverage allowance is specified.

A.3.5.5.5 Soda straw voids. There shall be no visible soda straw voids between the solder mask and the printed

board base material surface and the edges of the conductor patterns.

A.3.5.5.6 Solder mask cure. The cured solder mask coating shall not exhibit tackiness, blistering, or delamination.

A.3.5.5.7 Thickness. The solder mask thickness shall be as specified (see A.3.1.1).

A.3.5.6 Stiffeners.

A.3.5.6.1 Acceptability, design, and placement. The design, placement, and acceptability requirements for

stiffeners shall be as specified.

A.3.5.6.2 Bonding. Complete bonding of the stiffener to the flexible portion of the printed wiring board is not

required (see A.6.13). Unless otherwise specified (see A.3.1.1), the bonding of the stiffener to the flexible portion of

the printed wiring board shall be 50 percent minimum.