Reliability and Moldability of Epoxy Molding Compounds

  • 廖 祐慶

Student thesis: Doctoral Thesis

Abstract

Encapsulation molding compounds are commonly used to protect IC chips Their composition always contains fillers of a large amount (about 70%) and will affect the properties of the compounds Thus in order to clarify the filler effects three types of silica fillers including crystal silica edgeless silica and fused silica were studied experimentally to explore their effects on the compounds The results show that all of the flow spiral length glass transition temperature (Tg) coefficient of thermal expansion and water absorption rate of the encapsulation molding compounds decrease as the filler amount increases In contrast both thermal conductivity and flexural strength of the compounds increase as the filler amount increases For the three fillers the edgeless silica filler has the advantage of a large flow spiral length and can be molded better It also has a larger thermal conductivity larger flexural strength and lower water absorption rate。 When consider the effects of its size type and shape The results show that the filler with a larger particle size will have a smaller viscosity and will flow better; the spherical filler is better than the polygonal one in this respect In contrast both thermal conductivity and coefficient of thermal expansion increase slightly as the filler particle size increases ; the values of these two properties of crystal silica are about twice those of fused silica; the thermal conductivity of polygonal silica is larger than that of spherical silica On the other hand the dependence of the coefficient of thermal expansion on filler shape is not significant but is significant on filler type Also the degree of curing of the compound with polygonal silica is higher than that with either spherical or crystal silica That is curing is affected by both filler type and shape and can be tuned accordingly to suit the need EMCs were molded to Cu leadframes to experimentally quantify the effect of mold temperature resin viscosity leadframe oxidation and powder moisture on the adhesion force Component reliability was assessed by PCT A higher mold temperature result in a larger adhesion force The mold temperature of 175℃ provides the largest process window Leadframe oxidation can increase adhesion first but then decrease adhesion drastically with further oxidation The powder moisture content has mixed effect on adhesion Green flame retardants are required for protecting the electronic components human health and the environments In this study the effects of three green flame retardants of Triphenyl phosphine oxide Melamine cyanurate (MCA) and Aluminum hydroxide on the properties of encapsulation molding components were examined by experiments The results show that their amounts in weight percentage affect the encapsulation and flammability properties The flammability test results indicate that both Triphenyl phosphine oxide (with the added amount reaching 1 5% or more) and MCA (of 2% or more) can meet the UL94-V0 flammability requirement; but Aluminum hydroxide could not By adding more Triphenyl phosphine oxide the EMC moldability becomes poor and also induces large leakage current Adding more MCA will also lead to poor moldability but not increasing the leakage current Overall comparison indicates that either Triphenyl phosphine of 1 5 to 2 wt% or MCA of 2 to 3 wt% can be adopted as green flame retardants for encapsulation molding compounds for practical applications The metal particles embedded in the molding compound it is possible that the input/output pin of the IC can become electrically short due to particle bridging An experimental facility is built up to investigate the abrasive wear behavior of EMC particles The parameters explored include particle impacting velocity and impacting angle The results show that the erosion rate depends on both the particle impacting velocity and impacting angle A higher velocity will cause more erosion whereas a smaller impacting angle will cause more erosion especially at higher impacting velocities Furthermore the morphology of the eroded particles is irregular in shape and a smaller impacting angle will result in a larger dimension of the eroded particles Finally Especially to mention that the metal debris are always present in the EMC powders due to the hard silica fillers in the compound therefore have to be removed before molding Nd-Fe-B permanent magnets are used to remove these debris The results show that the metal debris can be removed effectively as the rate of accumulation of the metal debris increases as time proceeds in the removing operation The removal effectiveness of the debris is affected by both the magnetic flux density and the flow around the magnet The wake flow behind the magnet is a relatively low speed recirculation region which facilities the attraction of metal debris in the powders Thus the largest amount of the accumulated EMC powders occurs downstream of the magnet Hence this low speed recirculation region should be better utilized to enhance the removal efficiency of the metal debris
Date of Award2017 Aug 5
Original languageEnglish
SupervisorJung-Hua Chou (Supervisor)

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