Uniform solder coating on roughened substrate
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United States of America Patent
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Jan 12, 1993
Issued Date -
N/A
app pub date -
Feb 14, 1992
filing date -
Feb 14, 1992
priority date (Note) -
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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.
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