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Method for a solder ball dam for a BGA package

IP.com Disclosure Number: IPCOM000011732D
Publication Date: 2003-Mar-12
Document File: 4 page(s) / 201K

Publishing Venue

The IP.com Prior Art Database

Abstract

Disclosed is a method for a solder ball dam for a ball grid array (BGA) package. Benefits include improved performance and improved reliability.

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Method for a solder ball dam for a BGA package

Disclosed is a method for a solder ball dam for a ball grid array (BGA) package. Benefits include improved performance and improved reliability.

Background

              BGA solder joints can open and fail at the interface between the solder and the substrate pad because of solder fatigue after temperature cycling testing or shock and vibration testing. This failure is particularly pronounced with the following:

•             Solder mask defined pad (see Figure 1)

•             Metal defined pad (see Figure 2)

•             Electroless nickel immersion gold (Ni/Au) surface finish that cause brittle fracture at the Ni-P+ interface

•             Scaling down of the BGA ball size that increases interfacial stress, such as < 1mm BGA

              (These package designs are susceptible to stress from bending.)

•             Solder fatigue failure, which is more prone to happen at solder ball to component pad interface due to larger coefficient of thermal expansion (CTE) mismatch between the silicon die, such as controlled collapse chip collect (C4) mounted and underfilled, and the component substrate

              The conventional solutions to prevent BGA component solder joint fatigue are to use larger solder balls to maintain solder ball joint’s standoff and minimize in-plane shear stress at the interface. Ceramic column grid array (CCGA) was introduced to minimize interface shear stress and improve its reliability. However, for brittle fracture failure at the Ni-P+ interface, the containment solution has been to minimize the flexure of the BGA component during system assembly.

General description

              The disclosed method is a nonconductive dam around BGA solder balls. A layer of epoxy-filled silica glass surrounds the solder balls at the interface with a metal-defined substrate pad to redistribute the stress load.

              The key elements of the method include:

•             Layer of epoxy filled silica glass surrounding solder balls at the component interface

•             70-90% wt of silica glass in the coating layer

•             Coating height 0.2~0.5x...