Research On Stress Analysis And Modification Of Micro-electronics Device

The reliability of the electronic products has an important role in the whole electricindustry. The temperature of the electronic products always changes during the processand working condition. And, since different components of the electronic products aremade of different materials, their coefficients of thermal expansion （CTE） are withdifferent value, which gives rise to thermal-mechanical stress among differentcomponents. It makes the failure rate of the electronic products increase severely. Thenormal thermal-mechanical stress problems in the flip-chip and wire bonding these twopackaging technologies have been researched in this paper, respectively. And make anoptimization design for the material and structure of two kinds of typical devices.In the first part of the paper, we have studied the stress condition of die backside inthe Flip chip packaging technology. The possibilities of stress modification andmechanical property increasing by coating a thin nitride film layer （AlN or Si₃N₄） onthe die backside to protect the die have been discussed.We study related characterizations by combining the Three Point Bending Test（3PB） and Finite Element Analysis （FEA）. The details are shown as followed:1. The condition of the stress modification of the die backside. Stress of diebackside has been reduced after coating layer by comparing the stress beforeand after coating layer with the method of building FEA models, includingpower cycle condition, temperature cycle condition.2. The mechanical property of the die will be improved after coating layer.Coating a film layer on the die backside can increase the breaking strength ofthe silicon die, which has been verified by using3PB test machine to test thebreaking strength of the die wafer. The relationship between die wafer surfaceroughness and die wafer breaking strength has also been studied at the sametime, which indicates that the rougher surface is, the smaller breaking strengthis.3. The effect of the existing micro-crack which is in the silicon die backsidesurface. Generally, the die backside has some micro-crack which makes the stress and the breaking strength different from the models aforementioned. Westudy the condition which the silicon die has micro-crack in its backsidesurface by combining the relevant theories,3PB test and FEA method,verifying the advantage of coating layer in this situation.By using the different research methods in the study of the property of the silicondie after coating layer on the die backside, the results reveal that coating a hard nitridelayer on the die backside is a feasible way to protect the die fracture and protect thechip.In the second part of the paper, we have studied the effect of the structure andmaterial design of device to the reliability of the packaging in the wire bondingpackaging technology. The study concentrates on the analysis and optimization designof temperature dissipation and thermal-mechanical stress in the packaging. The studyincludes the following two parts:1. Structure design. The influence of structural design in the packaging to thethermal dissipation and stress distribution of the device has been studied byusing FEA method. Furthermore, the verification and optimization of thestructure in the production line have also been done.2. The chosen of the packaging material. Kinds of materials are used in theelectronic packaging. And different materials have different effects on thereliability problems of device, such as thermal dissipation, stress distribution.Some kinds of materials （die attach and molding compound） used in theproduction line have been compared in the effect of reliability problemsbrought by using different materials to make an optimization design to thereliability of device.By the researches aforementioned, we study the effect of the thickness of leadframe and die, the structure of the lead frame. At the same time, according to thesimulation and experiment results, the high quality and reliability could be achieved byusing Ag-resin as die attach and the compound which has higher glass transitiontemperature, smaller CTE and lower moisture absorption.