Browse Prior Art Database

Direct Chip Attach to Flex Substrates

IP.com Disclosure Number: IPCOM000108091D
Original Publication Date: 1992-Apr-01
Included in the Prior Art Database: 2005-Mar-22
Document File: 2 page(s) / 68K

Publishing Venue

IBM

Related People

Cox, AR: AUTHOR [+2]

Abstract

Disclosed is an improvement to a manufacturing process for attaching circuit chips to flexible connecting substrates. Alignment of chip and substrate is by viewing through the substrate; solder reflow is by in-situ focused infrared (IR) heating, all combined in a composite adjustment tool.

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Direct Chip Attach to Flex Substrates

       Disclosed is an improvement to a manufacturing process
for attaching circuit chips to flexible connecting substrates.
Alignment of chip and substrate is by viewing through the substrate;
solder reflow is by in-situ focused infrared (IR) heating, all
combined in a composite adjustment tool.

      A process has been used for attaching chips to substrates for
many years called "flip chip bonding".  By this method the mounting
of the chips is relatively easy to achieve on ceramic or hard card
substrates, but is much more difficult on flexible circuits, which
cannot be subjected to such high temperatures.

      The solder balls on chips normally consist of 95% to 97% lead
remainder tin, with a melting point around 310~C. A recently
introduced process uses substrate pads coated with eutectic solder
(MP > 200~C) which, on reflow in contact with the high lead solder,
forms a joint with no melting of the solder balls, the latter acting
merely as stand-off posts.  This process is adaptable to chip-on-flex
joining. The problem is one of aligning the chip to the flexible
substrate and keeping it in place while melting the eutectic solder;
heated flex expands and warps.  Placement of the chips is made even
more difficult using conventional flip chip placement tooling if the
surface of the solder on the substrate pads is not perfectly flat and
of uniform height.

      The alignment and reflow tooling improvement describe...