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Browse Prior Art Database

Solder Application Using Resist Mask

IP.com Disclosure Number: IPCOM000122063D
Original Publication Date: 1991-Oct-01
Included in the Prior Art Database: 2005-Apr-04
Document File: 1 page(s) / 56K

Publishing Venue

IBM

Related People

Ingraham, AP: AUTHOR [+4]

Abstract

A process has been developed to apply a low melting point solder of sufficient volume to FR-4 circuitized panels for joining chips with C4 solder bump interconnections. The uniqueness is that the photo resist mask used is strippable after exposure to a vapor phase solder reflow temperature. This allows an application of the proper quantity of paste on each panel joining pad and controlled composition of the solder.

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This is the abbreviated version, containing approximately 69% of the total text.

Solder Application Using Resist Mask

      A process has been developed to apply a low melting point
solder of sufficient volume to FR-4 circuitized panels for joining
chips with C4 solder bump interconnections.  The uniqueness is that
the photo resist mask used is strippable after exposure to a vapor
phase solder reflow temperature. This allows an application of the
proper quantity of paste on each panel joining pad and controlled
composition of the solder.

      The figure shows a select cross-section of a panel 1 designed
for subsequent direct joining of chips with solder bumps.  The top
surface of the panel has 5 mil diameter copper pads 2 in select areas
for solder bump attachment and a solder mask 3 covering the remaining
surface.  The volume of the well at each of the solder bump pad
openings, when filled with solder paste, is not sufficiently large
enough for the required solder needed for low temperature solder bump
attach.  To provide the proper size well for the solder paste, a
resist 4 is applied over the solder mask with an opening at each pad.
The critical property of the resist is that it must be strippable
after exposure to a solder reflow of 220~C.

      Typical dimensions for this structure would be a copper pad 2
thickness of 1.4 mils (1 ounce copper), solder mask 3 of 3 mils and a
resist 4 also 3 mils thick.  With an 8 mil diameter opening in the
solder mask and resist, a sufficient volume of solder paste will be
deposited in the well...