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Method for high flow, low stress molding compounds

IP.com Disclosure Number: IPCOM000012703D
Publication Date: 2003-May-21
Document File: 7 page(s) / 171K

Publishing Venue

The IP.com Prior Art Database

Abstract

Disclosed is a method for high flow, low stress molding compounds. Benefits include improved performance and improved functionality.

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Method for high flow, low stress molding compounds

Disclosed is a method for high flow, low stress molding compounds. Benefits include improved performance and improved functionality.

Background

        � � � � � Voids can form during the filling of large die flip-chip packages that have small bump pitch and gap height, such as 400-mm2 area with full array 120-µm pitch x 45-µm high bumps, with filled systems, such as with >70 wt%.

        � � � � � Voids can form during the underfilling and/or overmolding of molded matrix array package (MMAP) substrates that have large area molding arrays with high die density, such as 58 x 58‑mm arrays with >25 die per array.

        � � � � � ILD cracking, die tilt, and float can occur with flip-chip molded matrix array packages (FC MMAPs) using molded underfilling and low-K interlayer dielectric (ILD) silicon technology.

        � � � � � Excessive wire sweep can occur with stacked MMAP packages that have tight bond pad pitch and long wire lengths.

        � � � � � The capability to mold large area MMAP arrays that have high die density is an identified requirement.

        � � � � � The conventional solution for large die flip-chip package voiding is adopting conservative and commercially unacceptable design rules, such as limiting the die size, MMAP molding array density, and die gap/bump pitch. This solution is unacceptable because ancillary packaging concerns, such as underfilling, do not keep pace with growing market trends for smaller and thinner packages.

        � � � � � The conventional solution for MMAP underfilling/overmolding voiding is placing vent holes under the die. This solution is unacceptable because it uses valuable silicon surface routing space, diminishing product performance.

        � � � � � The conventional solution for ILD cracking, die tilt, and float is using vacuum assisted underfilling/molding. This solution is unacceptable because it is very expensive and has many processing and maintenance issues.

        � � � � � The conventional solution for excessive wire sweep with stacked MMAPs is using low molding pressures and transfer speeds. This solution is unacceptable due to excessive voiding and frequent partial fills.

� � � � � With conventional MMAP packaging technology, partially cured (B-staged) resins are transfer molded into various packaging configurations. Although this technology has found wide usage, it has several limitations related to the melt rheology of the material. The efficacy of the process is adversely affected when it is used for underfilling low-K ILD die, which are prone to cracking when subjected to mechanical loading during assembly operations. Additional problems occur when conventional materials are used for stacked wirebond packages, which have small mold caps, tight bonding pad pitches, and long wire lengths.

� � � � � MMAP molding compounds have melt viscosities of 10 to 35 Pa-s and require a substantial force to cause the material to flow into small gap areas, such as in underfilling (see Figure 1). Typically,...