Low Tg Epoxy Adhesives for Thermal Management

Abstract

The complexity of microelectronic circuits, their scale of integration, and clock speed re quirements have been increasing steadily. All of these changes have the effect of increasing the power density of the micro-circuits. IC's with a power of several watts and area of over a square centimeter are quite common. Thus, there is more heat generated per device at die, component, and substrate-attach levels of electronic packaging.In order to maintain reliability of finished products, the junction temperature of the con stituent devices must be kept low. It has been demonstrated that thermal management can be one key to lowering the cost and increasing the performance life of microelectronic products. The cost effectiveness of lowering device temperature has been demonstrated to be dramatic in comparison to the cost of thermal management materials(l,2).Proper thermal management of advanced microelectronic devices has to be addressed at all levels. One should address the problem from the basic level of die-attach, through com ponent attach, and eventually substrate-attach to thermal drains.Thermal management is almost invariably coupled with a thermally induced stress problem. The increase in temperature at the device level also means a larger fluctuation of tempera ture from the ambient. Each cycle of on-off for the device represents one thermal cycle. Stress induced failures due to coefficient of thermal expansion (CTE) mismatch is much more acute for higher power devices.In this paper, we will also address the thermally induced stress on the microelectronic product at all levels of packaging with major emphasis on component and substrate levels.We will demonstrate various ways and examples of reducing or eliminating this stress, which is a major cause of device failures. One of the proven methods is through the use of low Tg epoxies with high thermal stability.

Thermal Effects of Replacing Solder with Conductive Adhesives

“…Even if the TCE of the adhesive is increased, the stress level of bonded assemblies is reduced since the adhesives are extremely flexible. 1 Adhesive D has a glass transition point lower than 0°C.…”

“…Successful assembly with proper thermal management of the device must include good thermal dissipation and mechanical stress reduction. 1 Several stress analyses have dealt with the problem of die bonding. The two-dimensional model 2 predicts that die stress increases with increasing:…”

Reliability issues of replacing solder with conductive adhesives in power modules

“…A first order approximation of the stresses is presented in Table I. The stresses at the interface according to adhesive elasticity [2] were calculated from the formula:…”