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Method for reinforced wire bonds

IP.com Disclosure Number: IPCOM000021638D
Publication Date: 2004-Jan-28
Document File: 3 page(s) / 96K

Publishing Venue

The IP.com Prior Art Database

Abstract

Disclosed is a method for reinforced wire bonds. Benefits include improved functionality and improved performance.

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Method for reinforced wire bonds

Disclosed is a method for reinforced wire bonds. Benefits include improved functionality and improved performance.

Background

Wire sweep can cause wire shorting or breakage during molding compound encapsulation for very fine pitch wire-bonded electronic packages.

         The conventional trend in stack-dies for flash packages for wire-bond components is toward smaller pitch using longer, smaller diameter wire with multiple loops. Wire sweep during encapsulation molding is becoming a critical issue. The prevention of wire sweep during molding encapsulation must be resolved.

Conventional solutions include the following:

•         Modifying the molding compound matrix (typically, epoxy) to reduce its viscosity to promote easier flow and minimize the wire sweeping effect

•         Reducing the silica filler mesh size and optimizing the silica filler percentage to minimize wire sweep, while minimizing CTE mismatch and retaining mechanical strength

•         For injection molded packages, optimizing the molding-gate location to minimize wire sweep

•         Optimizing the wire bonding sequence and bond-pad arrangement to minimize wire length to reduce wire sweep

The conventional solutions, however, limit the wire bond parameters, which limit the number of stack dies and restrict the wire bond arrangement and molding gate orientation for small form factor components.

The conventional industry practice is a maximum wire sweep of <5% to prevent electrical shorting. For a 45-µm in-line pad pitch with a 0.7-mils gold wire diameter, the maximum wire length is 150 mils or less (see Figure 1).

General description

The disclosed method reinforces the wire surface to prevent wire sweep or wire shorting during encapsulation for fine pitch wire-bond electronic packages.

         The key elements of the method include:

•         Reinforcing the wire surface by coating the outer surface with a layer of thermoset material through thermal spraying and a curing process

•         Coating thickness of about ~10%-20% of the wire diameter to ensure sufficient reinforcement prior to the encapsulation molding process

•         Thermoset material in compliance to the wire surface and encapsulation molding mate...