Browse Prior Art Database

Hydrogen Overvoltage Suppression in Solder Decal Plating

IP.com Disclosure Number: IPCOM000104076D
Original Publication Date: 1993-Mar-01
Included in the Prior Art Database: 2005-Mar-18
Document File: 2 page(s) / 59K

Publishing Venue

IBM

Related People

Hayden, TF: AUTHOR [+3]

Abstract

Solder decals are used for applying controlled amounts of (typically eutectic) tin/lead solder to sites on circuit carriers to allow the attachment of C4 chips. In the typical process for producing solder decals, photoresist is applied to a stainless steel substrate, imaged and developed to produce a pattern of holes which correspond to the chip C4 footprint. Tin/lead solder is then electroplated into these cavities and the photoresist removed. The pattern of solder deposits on the stainless steel substrate (termed a "solder decal") can then be thermally transferred to the circuit carrier. During the transfer process, solder dewets from the stainless steel substrate and wets (typically) copper pads or lines on the circuit carrier.

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Hydrogen Overvoltage Suppression in Solder Decal Plating

      Solder decals are used for applying controlled amounts of
(typically eutectic) tin/lead solder to sites on circuit carriers to
allow the attachment of C4 chips.  In the typical process for
producing solder decals, photoresist is applied to a stainless steel
substrate, imaged and developed to produce a pattern of holes which
correspond to the chip C4 footprint.  Tin/lead solder is then
electroplated into these cavities and the photoresist removed.  The
pattern of solder deposits on the stainless steel substrate (termed a
"solder decal") can then be thermally transferred to the circuit
carrier.  During the transfer process, solder dewets from the
stainless steel substrate and wets (typically) copper pads or lines
on the circuit carrier.

      During the electroplating process, using methane sulfonic acid
based tin and lead compounds and electrolyte, a phenomena occurs
which is detrimental to uniform bump formation and bump retention on
the stainless substrate.  A condition commonly referred to as
hydrogen overvoltage or gassing produces gas pockets at the
solder/stainless steel interface.  The resulting "solder bumps" then
do not have full interfacial contact with the stainless surface which
makes them more susceptible to dislocation during the process of
removing photoresist.  Since the gas pockets can be of different
sizes, the solder bumps can assume different solder volumes, which
lead to an undesirable variability in the amount of solder applied to
the circuit carrier sites.  Remedies, such as reducing the current
density at wh...