Uniform solder coating on roughened substrate

Details Uniform solder coating on roughened substrate Uniform solder coating on roughened substrate

1992-02-14

1993-01-12

Zimmerman, John

Stock material or miscellaneous articles

All metal or with adjacent metals

Microscopic interfacial wave or roughness

428647, 228203, 427309, 427328, B32B 330, B23K 120, B05D 310

Patent

active

051789655

ABSTRACT:
A roughened surface of a conductive substrate, such as copper, provides uniform Sn-Pb solder coatings and improved solder retention at printed wiring board (PWB) plated through-hole rims (knees) and surface pads during solder dipping or reflow. A high density of copper surface features of moderate average roughness provides the most favorable solder coating thickness distribution. Various chemical or electrochemical etching processes may be used to produce the desired copper surface topography. Reflowed solder thickness distribution in a PWB knee region attained with a ferric chloride copper etching process peaks at 4 .mu.m, which provides a good margin of safety for preventing exposure/oxidation of the underlying Cu-Sn intermetallics. The ferric chloride copper etching process yields only 1% of solder thickness measurements in the undesirable 0-1.5 .mu.m range for plated through-hole rims. Copper surface roughening is expected to greatly reduce solderability loss in mass produced PWBs. In addition, solder bearing on PWB surface pads is avoided with copper surface roughening so that alignment of surface mount component leads prior to soldering is greatly facilitated.

REFERENCES:
patent: 3562039 (1971-02-01), Strohmayer
patent: 4027055 (1977-05-01), Schneble
patent: 4127438 (1978-11-01), Babcock et al.
patent: 4373656 (1983-02-01), Parker et al.
patent: 4767049 (1988-08-01), Butt et al.

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