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.

Pages 1 - 2 - 3 - 4 - 5 - 6 - 7 - 8 - 9 - 10 - 11 - 12

MIL�PRF�50884F

APPENDIX A

TABLE A�III. Thickness of conductors without copper plating (after processing).

Minimum surface conductor

Starting copper

Processing reduction

thickness (after processing)

foil weight

allowance

Inches (μm)

inches (μm)

1/8

.00006 (1.5)

.00012 (3.048)

1/4

.00006 (1.5)

.00024 (6.096)

3/8

.00006 (1.5)

.00037 (9.398)

1/2

.00016 (4.0)

.00045 (11.43)

.00024 (6.0)

.00098 (24.892)

.00024 (6.0)

.00219 (55.6)

.00024 (6.0)

.00341 (86.6)

.00024 (6.0)

.00463 (117.6))

A.3.6.2.3 Conductor width. The conductor width shall be as specified (see A.3.1.1).

A.3.6.2.4 Annular ring, internal (see figure G�6). The minimum annular ring for functional internal lands on types 3

and 4 printed wiring boards shall be as specified (see A.3.1.1). If not specified on the applicable master drawing, the

minimum internal annular ring should not be less than the values specified in the IPC's 2220 series of documents for

the design of flexible or rigid-flex printed wiring boards.

A.3.6.2.5 Bonding of conductor to base material and lifted lands (see figure G�7).

A.3.6.2.5.1 Non-stressed specimens (as received condition). There shall be no lifted lands, or evidence of lifted

lands on the non-stressed microsectioned test specimen. When inspected in accordance with A.4.8.2 and lifted lands

are present, the lot shall be 100 percent visually inspected in accordance with A.4.8.1 for separation of the lands from

the base material.

A.3.6.2.5.2 Stressed specimens (after rework simulation, resistance to soldering heat, or thermal shock). After

undergoing rework simulation, resistance to soldering heat, or thermal shock testing (see A.3.7.4.8, A.3.7.6.2, and

A.3.7.6.3), the maximum allowed distance from the base material surface to the bottom of the edge of the land or pad

shall be no greater than the total land thickness. The total land thickness is equal to the combined thickness of the

metal foil and copper plating on that land.

A.3.6.2.6 Undercutting. Undercutting at each edge of the conductors shall not exceed the total thickness of the

copper foil and plated copper.

A.3.6.3 Hole preparation prior to metallization. The presence of both flexible and rigid base materials in type 4

designs will cause varying degrees of etchback amongst the various base materials in the finished plated-through

hole. In addition, all designs that make use of adhesiveless flexible base material will typically exhibit minimal

etchback at the flexible dielectric to copper conductor interface.

A.3.6.3.1 Desmear (hole cleaning) (see figure G�8). When etchback is not specified on the applicable master

drawing, the vertical faces of the internal conductors of holes that will be plated shall be cleaned to be free of resin

smear. Lateral removal of base material from the hole wall shall not exceed .001 inch (0.03 mm). When desmear is

used for hole preparation, a negative etchback of .0005 inch (0.013 mm) maximum shall be acceptable.