Thermomechanical properties of 1C molding compounds

Abstract

Eight commercial semiconductor grade epoxy compounds that are used to encapsulate 1C (integrated circuit) devices have been evaluated for their ability to minimize the development of thermal stresses which can cause failure during device temperature cycling. Thermal expansion, dynamic modulus and adhesion studies are used to describe the mechanical interaction between the plastic package and the silicon device it surrounds. A “figure of merit” is defined for the development of stress on the 1C device as it is cooled after the packaging process. The stress is shown to be proportional to the product of three terms: (αp‐αs) Ep (Tanch‐T) where αp and αs are the expansion coefficients for the plastic and silicon, respectively, Ep is the modulus of the epoxy and Tanch is the temperature at which the epoxy becomes anchored to the silicon device during transfer molding. In addition, the importance of good adhesion between the epoxy encapsulant and the silicon device to prevent package cracking has been demonstrated by finite element analysis and a novel adhesion test.

Kinetics study of imidazole-cured epoxy-phenol resins

“…Molding compounds need to have much more stringent properties like higher thermal resistance, higher moisture resistance, lower thermal expansion coefficient, and lower modulus. 4 Encapsulants formulated out of epoxy-phenol resins are transfer-molded to form the protective shell outside integrated circuits. During the polymerization, the molecular weight increases and the crosslinked structure builds up, which governs the rheological and mechanical properties of the cured resins.…”

Evolution of residual stresses with fatigue crack growth in integral structures with crack retarders

“…The stress-free temperature often coincides with the glass transition temperature (T g ) [16] if the adhesive is cured above T g . For a system where T g is above the curing temperature, T sf is taken to be equal to the curing temperature (T c ) [17]. Hence, in this work the induced thermal residual stresses have been modelled applying the temperature drop defined below, since the T g [6] nearly coincides with the curing temperature (T c ):…”

Evaluating IC-package interface delamination by considering moisture-induced molding-compound swelling

“…The stress intensity factor of a moisturized package at high temperature is expressed by he sum of the stress intensity factor (due to thermal stress caused by heating from molding temperature ) and the change in stress intensity factor due to the swelling of the molding compound. That is (1) Interface delamination in a moisturized package occurs when exceeds the true adhesion strength after exposure to moisture, To examine the above-mentioned evaluation method, the change in stress intensity factor due to the swelling was calculated. Fig.…”

“…In these soldering processes, the package is heated up to above 200 C. If the molding compound has absorbed moisture, package cracking may occur during the reflow soldering. These cracks are caused by vapor pressure generated in the space between the die pad and the molding compound [1], [3]. Because the prediction of interface delamination in a moisturized package was difficult, package design to prevent package cracking has been conducted by allowing interface delamination [3].…”