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Self Aligning Assembly for Small Parts

IP.com Disclosure Number: IPCOM000073495D
Original Publication Date: 1970-Dec-01
Included in the Prior Art Database: 2005-Feb-22
Document File: 1 page(s) / 12K

Publishing Venue

IBM

Related People

Garwin, RL: AUTHOR

Abstract

It has been noted that the C-4 joining technique (controlled-collapse chip connection technique) allows chips to be placed on a module with considerably less accuracy than is required of the final positioning.

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Self Aligning Assembly for Small Parts

It has been noted that the C-4 joining technique (controlled-collapse chip connection technique) allows chips to be placed on a module with considerably less accuracy than is required of the final positioning.

In the C-4 technique, the semiconductor chip is supplied with a substantial number of ball-like solder contacts. The solder is applied by evaporation through a metal mask or by normal plating techniques onto areas delimited by photoresist. After the chip is cleaned, it is heated to alloy the lead and tin and to form solder into ball-like projections. On the module, the connection pads have been provided with a solder plating, but the pad is isolated against solder flow down the conducting line by means of a glass dam sprayed and fritted over the conductor beyond the pad. Naturally, if there are more than three solder projections on the chip, it is likely that but three will contact the pads when the chip is assembled onto the module. However, as the assembled chip and module are heated, the solder fuses and surface tension reduces the spacing between chip and module, bringing into contact all molten solder balls on the chips with the metallic lands on the module. With a surface tension of perhaps 1000 dynes per centimeter, the excess pressure inside a solder ball of 1 mil radius is almost 1 atmosphere. If the chip is misaligned with the module, the solder bridges after they form, tend to reduce their length in order to minimize the surface area of solder, thereby exerting a very strong self-aligning force on the modul...