Browse Prior Art Database

UV Imaged Reworkable Encapsulent for Fatigue Life Enhancement

IP.com Disclosure Number: IPCOM000112392D
Original Publication Date: 1994-May-01
Included in the Prior Art Database: 2005-Mar-27
Document File: 2 page(s) / 35K

Publishing Venue

IBM

Related People

Crockett Jr, CH: AUTHOR [+4]

Abstract

High DNP (distance from zero-stress point) modules often require an encapsulent to meet fatigue life and/or failure rate objectives. A UV-imaged encapsulent which can be easily reworked is disclosed. Ease of application, low cost and reworkability are key attributes. This invention applies to any ball-grit-array type module. A UV imaged and cured liquid resin is applied to the module so that 75 - 100% of each solder ball is covered. The module is then dried to remove solvent. Artwork with an array of dots is aligned with the encapsulated solder balls. The resin is imaged and developed. The encapsulent which was exposed to the UV light remains, while the encapsulent under the artwork does not cross-link, and therefore is removed at the developing step.

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UV Imaged Reworkable Encapsulent for Fatigue Life Enhancement

      High DNP (distance from zero-stress point) modules often
require an encapsulent to meet fatigue life and/or failure rate
objectives.  A UV-imaged encapsulent which can be easily reworked is
disclosed.  Ease of application, low cost and reworkability are key
attributes.  This invention applies to any ball-grit-array type
module.  A UV imaged and cured liquid resin is applied to the module
so that 75 - 100% of each solder ball is covered.  The module is then
dried to remove solvent.  Artwork with an array of dots is aligned
with the encapsulated solder balls.  The resin is imaged and
developed.  The encapsulent which was exposed to the UV light
remains, while the encapsulent under the artwork does not cross-link,
and therefore is removed at the developing step.  This creates a
solderable surface free of polymer contamination at the bottom of
each ball.  The module can then be soldered to a card using a
standard Surface-Mount Technology (SMT) process.  The encapsulent
restricts wetting up the sides of the ball and creates tall, columnar
joints which are known to enhance fatigue life.  The rigid
encapsulent prevents premature cracking of the solder joint at the
module, further enhancing fatigue life.  Rework is accomplished using
the standard processes, as the encapsulent does not adhere to the
carrier .  The application, assembly, and rework processes use no new
tools, and the encapsulent can...