MILPRF55110G
APPENDIX A
c.
For ball grid array lands, the following shall apply:
(1) If the land is solder resist defined, allowable misregistration of the solder resist causes breakout of the
land of not more than 90 degrees.
(2) If the land is copper defined, the solder resist shall not encroach onto the land. Solder resist on the
land-to-via connecting conductor shall be acceptable.
(3) If solder resist dam is specified, the dam remains in place with the conductor to the via covered.
d.
Edge-board contacts and test points which are intended for assembly testing shall be free of solder resist
unless a partial coverage allowance is specified.
A.3.5.7.4
A.3.5.7.4 Thickness (see figure A4). The solder resist thickness shall be as specified (see A.3.1.1).
A.3.5.7.5
A.3.5.7.5 Solder resist cure. The cured solder resist coating shall not exhibit tackiness, blistering, or delamination
in excess of that allowed in A.3.5.7.1.
A.3.6
A.3.6 Plated hole requirements. When plated holes are examined by microsection, the test specimen shall meet
the requirements of A.3.6.1 through A.3.6.15. IPC-A-600 contains figures, illustrations, and photographs that can aid
in the visualization of internally observable accept/reject conditions of microsectioned test specimens. If a condition is
not addressed herein or specified on the master drawing, it shall comply with the class 3 criteria of IPC-A-600.
A.3.6.1
A.3.6.1 Annular ring, internal (see figure A5). The minimum annular ring for functional internal lands on type
printed wiring boards shall be as specified (see A.3.1.1). If not specified on the master drawing, the minimum internal
annular ring shall not be less than .002 inch (0.051 mm). Hole breakout shall not be acceptable.
A.3.6.2
A.3.6.2 Minimum external conductor thickness (types 2 and 3). The external conductor thickness shall be as
specified (see A.3.1.1). When an external conductor thickness is specified, the conductor thickness (copper foil and
copper plating) shall be equal to, or greater than, the specified thickness. When a conductor thickness with tolerance
is specified, the external conductor thickness (copper foil and copper plating) shall be within the specified tolerance
for the specified thickness. If nothing is specified, the limits for external conductors with plating defined in the
"External conductor thickness after plating" table of IPC-2221 shall apply.
A.3.6.3
A.3.6.3 Minimum internal conductor thickness (type 3) and external thickness (type 1). The internal conductor
thickness shall be as specified (see A.3.1.1). When a copper foil weight requirement is specified, a reduction in
thickness up to 10 percent below the minimum allowable foil thickness specified by the applicable material
specification shall be considered acceptable in order to accommodate a processing allowance for cleaning either by
chemical or mechanical means. If the master drawing specifies a minimum conductor thickness for internal
conductors, the resulting conductor shall be equal to or within the specified tolerance for the specified conductor
thickness. If nothing is specified, the limits for internal layer foil thickness after processing defined in the "Internal
layer foil thickness after processing" table of IPC-2221 shall apply.
A.3.6.4
A.3.6.4 Dielectric layer thickness (see figure A6). The minimum dielectric thickness separating the conductor
layers of the printed wiring boards shall be as specified (see A.3.1.1). If not specified on the master drawing, the
minimum dielectric spacing base materials shall not be less .0035 inch (0.089 mm).
A.3.6.4.1
A.3.6.4.1 Heatsink planes (see figure A7). Radial cracks, wicking, or voids in the dielectric material used to
insulate the heatsink plane, or metal core, from circuitry and plated through holes, shall not reduce by 75 percent the
specified lateral spacing between adjacent conductive surfaces. Unless otherwise specified (see A.3.1.1), the
minimum lateral spacing between adjacent conductive surfaces, nonfunctional lands, or plated-through hole and the
heatsink plane shall be .004 inch (0.102 mm).
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