Browse Prior Art Database

Known Good Dye Test and Direct Chip Attach Assembly

IP.com Disclosure Number: IPCOM000117940D
Original Publication Date: 1996-Jul-01
Included in the Prior Art Database: 2005-Mar-31
Document File: 4 page(s) / 145K

Publishing Venue

IBM

Related People

Hoebener, KG: AUTHOR [+2]

Abstract

Disclosed is a technique to deposit low melt solder on the chip C4 bump using an inexpensive method. Having a controlled deposit of low melt solder on the chip C4 pads allows: 1. assembly of the chip to a test carrier for electrical test and burn-in or, 2. assembly of the chip to an organic carrier.

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Known Good Dye Test and Direct Chip Attach Assembly

      Disclosed is a technique to deposit low melt solder on the chip
C4 bump using an inexpensive method.  Having a controlled deposit of
low melt solder on the chip C4 pads allows:  1.  assembly of the chip
to a test carrier for electrical test and burn-in or, 2.  assembly of
the chip to an organic carrier.

      This process uses a diced chip with high temperature tin lead
C4 bumps (3/97 % SnPb).

      Low temperature solder paste containing no clean flux is
applied to a flat surface, several methods can be used.  One possible
method uses a doctor blade (Fig. 1) across a flat metallic or ceramic
plate.  another method uses a plate with a cavity and leveling with a
flat blade.  The solder paste depth should not exceed 2.5 mils.  The
solder paste is low melt tin lead (60/40 % SnPb), the paste is
thinned using a solvent in the paste, solvent will vary depending on
what solder paste is used.  Thinning the solder paste is used to
provide uniformity and promote adhesion.

      The next step is to place each chip in the solder (Fig. 2)
allowing sufficient time for all bumps to be coated with solder
paste.  The chip can sit in the solder paste since it will not
submerge further than 1 to 2.5 mils depth.  The typical C4 chip bump
height is between 4 and 5 mils.  With this height the chip surface
will not contact the solder paste.  After solder paste apply, the
chip is placed bumps down on a non-solderable flat sheet such as
aluminum, molybdenum or glass (Fig. 3) and sent through a low
temperature reflow.  The low melt solder will remain on the lower
portion of the chip bump (Fig. 4).  The reflow profile must allow the
low melt solder to reflow but must also be controlled to minimize
dissolution into the high melt metal...