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Method for a sliding fillet fork to control overmold as underfill flow to stop die/substrate gap voiding during molding

IP.com Disclosure Number: IPCOM000007806D
Publication Date: 2002-Apr-24
Document File: 5 page(s) / 93K

Publishing Venue

The IP.com Prior Art Database

Abstract

Disclosed is a method for a sliding fillet fork to control overmold as underfill (OMUF) flow to stop die/substrate gap voiding during molding. Benefits include improved reliability

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Method for a sliding fillet fork to control overmold as underfill flow to stop die/substrate gap voiding during molding

Disclosed is a method for a sliding fillet fork to control overmold as underfill (OMUF) flow to stop die/substrate gap voiding during molding. Benefits include improved reliability.

Background

              The conventional transfer underfill process for a matrix molded area package (MMAP) involves the use of a mold compound to underfill and overmold the package in a single step. In the conventional package configuration, several die are arranged on a strip of substrate (see Figure 1). Underfilling and overmolding are performed in one process step. The strip is sawed into single packages.

              The flow velocity of the molding material in the package is represented by the equation:

      This equation contains the following values:

§         −Pressure drop applied across the cavity

§         µ−Melt viscosity of the mold compound

§         −Flow speed or the velocity of the flow front

§         −Cavity length

§         d−Gap height

              The flow velocity in the package, v, is related to the gap height d. The flow velocity under the die is slow due to the small gap height, d1 (see Figure 2). The flow speed at the sides and top of the die is fast due the large gap (d2 and d3) when the flow is unrestricted. As a result, the flow wraps around the die and traps air in the die/substrate gap causing voids under the die (see Figure 3). The presence of voids in the die/substrate gap decreases the reliability of the package.

              Conventional solutions include:

§         Vacuum-assist molding – creating a vacuum in the mold to eliminate the presence of trapped air

§         Vented substrate – placing a substrate vent at the die paddle enables the air to escape

General description

              The disclosed method includes directing the flow of OMUF in a MMAP using mechanical means. A sliding fillet fork is placed on top of the strip. Initially, the mold material is directed to flow under the die/substrate gap for underfilling. Then the mold material backflows and pushes the sliding fillet fork to the direction of the gate. As a result, the material i...