Browse Prior Art Database

Reinforcement of C4 Solder Balls on Chips Used in Shear Applications

IP.com Disclosure Number: IPCOM000113383D
Original Publication Date: 1994-Aug-01
Included in the Prior Art Database: 2005-Mar-27
Document File: 2 page(s) / 36K

Publishing Venue

IBM

Related People

Frankeny, JA: AUTHOR [+2]

Abstract

Disclosed is a means of strengthening solder ball connects on electronic devices which are installed in shear applications. In a high density packaging design (*), chips are inserted under force against a circuit pad on a printed wiring board to assure good electrical contact of chip solder balls to the carrier electrical pads (Fig. 1). The force transmitted to the chip is transferred to the solder balls, resulting in their deformation. Depending on the strength of the interface between the solder ball and the chip, this application of force can result in breakage of the joint and loss of the solder ball, rendering the chip useless. Additionally, unsupported solder balls can creep over time, lessening the contact force and resulting in an increase in contact resistance.

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Reinforcement of C4 Solder Balls on Chips Used in Shear Applications

      Disclosed is a means of strengthening solder ball connects on
electronic devices which are installed in shear applications.  In a
high density packaging design (*), chips are inserted under force
against a circuit pad on a printed wiring board to assure good
electrical contact of chip solder balls to the carrier electrical
pads (Fig. 1).  The force transmitted to the chip is transferred to
the solder balls, resulting in their deformation.  Depending on the
strength of the interface between the solder ball and the chip, this
application of force can result in breakage of the joint and loss of
the solder ball, rendering the chip useless.  Additionally,
unsupported solder balls can creep over time, lessening the contact
force and resulting in an increase in contact resistance.

      As a means of strengthening the solder balls against creep,
deformation, and breakage, this disclosure recommends the use of a
polymer adhesive or encapsulant to form a fillet along the backside
of the solder balls as shown in Fig. 2.  Alternatively, the
encapsulant could also wick completely around the base of the solder
ball.  This solution is effective in improving the integrity of the
joint between the solder ball and chip and is an approach which is
low cost and automatable.

Reference

(*) European Patent 93,308,798.3.