Browse Prior Art Database

Encapsulation Mechanical Rework Technique

IP.com Disclosure Number: IPCOM000108697D
Original Publication Date: 1992-Jun-01
Included in the Prior Art Database: 2005-Mar-22
Document File: 2 page(s) / 70K

Publishing Venue

IBM

Related People

Gould, DJ: AUTHOR [+4]

Abstract

The concept outlined in this disclosure is that of mechanically removing an encapsulated surface mounted chip or module from an electronic circuit board. Encapsulation of surface mount components dramatically improves solder joint life. To date, no rework procedure has been shown to work effectively. The technique is proposed to work in removing an assembly from the middle of a board without disturbing the neighboring assemblies. The mechanism for removing the assembly is a specially designed diamond wire saw (see figure).

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Encapsulation Mechanical Rework Technique

       The concept outlined in this disclosure is that of
mechanically removing an encapsulated surface mounted chip or module
from an electronic circuit board.  Encapsulation of surface mount
components dramatically improves solder joint life.  To date, no
rework procedure has been shown to work effectively.  The technique
is proposed to work in removing an assembly from the middle of a
board without disturbing the neighboring assemblies.  The mechanism
for removing the assembly is a specially designed diamond wire saw
(see figure).

      The diamond wire (3 to 15 mils in diameter) and drive mechanism
are purchased from Laser Technology, Inc., North Hollywood, CA.  The
rest of the saw is designed for module removal.  This design requires
small pulleys on either side of the cutting area to allow removal of
encapsulated assembly without disturbing the neighboring assemblies.
The support arms for these pulleys are adjustable to accommodate
different size assemblies.  The height of the wire cut from the
surface of the circuit board is adjusted by the Z motion of the
table, the depth of the wire groove in the small pulleys or the use
of a pressure foot below the pulleys. This height should be adjusted
to leave approximately 2 to 5 mils of eutectic solder and
encapsulation above the copper lines on the circuit board.

      It is proposed that smoothness of the diamond wire cut will be
adequate for the rejoining of a...