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Pad on Solder Ball Structure which Allows for Ball Diameter Variation

IP.com Disclosure Number: IPCOM000113604D
Original Publication Date: 1994-Sep-01
Included in the Prior Art Database: 2005-Mar-27
Document File: 2 page(s) / 39K

Publishing Venue

IBM

Related People

Frankeny, JL: AUTHOR [+3]

Abstract

Disclosed here is a pad geometry to solve the problem of the connection of solder ball interconnects to pads plated with palladium dendrites. Since there is an unavoidable variation in the heights of the balls on the substrates certain balls, which are smaller than their neighbors, will not contact the dendites on their mating pad if the dendrites are plated on to flat pads, as shown in Fig. 1. A pad geometry is needed which allows for ball height variation and accommodates it without loss of contact. The solution disclosed here is uses the fact that in etching undercutting of the etch mask can occur and can be used to form a cross-shaped dished out area on the top of the pad (Fig. 2). This area could be a simple concave surface or could be produced to give either a raised or depressed cruciform shape as seen in Fig. 3.

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Pad on Solder Ball Structure which Allows for Ball Diameter Variation

      Disclosed here is a pad geometry to solve the problem of the
connection of solder ball interconnects to pads plated with palladium
dendrites.  Since there is an unavoidable variation in the heights of
the balls on the substrates certain balls, which are smaller than
their neighbors, will not contact the dendites on their mating pad if
the dendrites are plated on to flat pads, as shown in Fig. 1.  A pad
geometry is needed which allows for ball height variation and
accommodates it without loss of contact.  The solution disclosed here
is uses the fact that in etching undercutting of the etch mask can
occur and can be used to form a cross-shaped dished out area on the
top of the pad (Fig. 2).  This area could be a simple concave surface
or could be produced to give either a raised or depressed cruciform
shape as seen in Fig. 3.  The curve of the dished out or concave area
is such that larger balls will contact the dendrites on their mating
pad and will be pierced by the dendrites, while the smaller balls
will contact at the tips of the dendrites, still, however, making
good electrical contact.  This is shown in Fig. 4.