In this paper, thermomechanical and rheological properties of nonconductive pastes (NCPs) depending on silica filler contents and diluent contents were investigated. And then, thermal cycling (T/C) reliability of flip chip assembly using selected NCPs was verified. As the silica filler content increased, thermomechanical properties of NCPs were changed. The higher the silica filler content was added, glass transition temperature (T g) and storage modulus at room temperature became higher while coefficient of thermal expansion (CTE) decreased. On the other hand, rheological properties of NCPs were significantly affected by diluent content. As the diluent content increased, viscosity of NCP decreased and thixotropic index increased. However, the addition of diluent deteriorated thermomechanical properties such as modulus, CTE, and T g. Based on these results, three candidates of NCPs with various silica filler and diluent contents were selected and used as adhesives for reliability test of flip chip assemblies. T/C reliability test was performed by measuring changes of NCP bump connection resistance. Results showed that flip chip assembly using NCP with lower CTE and higher modulus exhibited better T/C reliability behavior because of reduced shear strain in NCP adhesive layer. Index Terms-Diluent, filler, flip chip, nonconductive paste (NCP), reliability, stud bump, thermal cycling (T/C). I. INTRODUCTION A S ELECTRONIC packaging technology trends move toward lower cost, fine pitch, higher electrical performance and better reliability, flip chip technology gains popularity as one of the best chip packaging candidates to meet these trends. Although flip chip assembly using solder balls is in the main stream of flip chip technology, flip chip assemblies using polymer conductive adhesives such as isotropic conductive adhesives (ICAs), anisotropic conductive films (ACFs), and nonconductive pastes (NCPs) have been under development because of their potential advantages compared with solder

In this article, embedded capacitor pastes (ECPs) with various BaTiO 3 (BTO) powder contents were formulated and screen-printed on PCBs to fabricate capacitors. The material properties of the ECPs that included their rheology, curing behavior, and dielectric constant were investigated. Embedded capacitors were fabricated for reliability tests related to the thermal cycling and high temperature and humidity potential of optimized ECPs. Additionally, changes in the dielectric properties were discussed. ECPs were formulated with various powder contents from 0 to 70 vol %. ECP resin was cured at temperatures ranging from 130 to 2208C. All ECPs had the viscosities below 30 Pa Á s at a shear rate of 100 s À1 to be easily screen-printable. The dielectric constant of the cured ECPs increased to 60 at 70 vol %, and the dielectric loss was approximately 0.023 for all ECPs regardless of BTO volume content. For the reliability test, ECPs with 50, 60, and 70 vol % BTO powder contents were selected and embedded capacitors were fabricated. After a thermal cycling test with a temperature range from À55 to 1258C for 1000 cycles, capacitance decreased by approximately 5 $ 10%, but the dielectric loss did not change. After a 858C/ 85RH% test for 1000 h, the capacitance and dielectric loss increased by nearly 20%. Cyanoresin (CRS) was used to form the high dielectric polymer/ceramic composite material. The newly formulated resin system had a dielectric constant that is double that of a conventional epoxy resin system. Additionally, the dielectric constant of the polymer/ceramic composite material increased 50% at 50 vol %.

EpoxylBaTiO3 composite embedded capacitorfilms (ECFs) were newly designedfor high dielectric constant and low tolerance (less than +5%o) embedded capacitorfabricationfor organic substrates. In terms of materialformulation, ECFs are composed ofspeciallyformulated epoxy resin and latent curing agent, and in terms ofcoating process, a comma roll coating method is usedfor uniform film thickness in large area. Dielectric properties ofBaTiO3(BT)& SrTiO3 (ST)composite ECF is measured MIM capacitors with oxygen plasma etched ECFs on 0X10 cm PCBs. For JX1 mm capacitors with 12 um thickness and 50 vol.0 %BTO ECFs, dielectric constant of39, dielectric loss of0. 01 7, capacitance density of2.4 nF/cm2, and less than 10% tolerance were obtained. Dielectric constant ofBTECF is bigger than that ofSTECF, and it is due to difference ofpermittivity ofBT and SrTiO3 particles.Dielectric constant ofBT & ST ECF in highfrequency range (0. 5-l OGHz) is measured using a cavity resonance method. In order to estimate dielectric constants at highfrequency, the reflection coefficient is measured with a network analyzer. Dielectric constant is calculated by observing thefrequencies ofthe resonant cavity modes. Although there was no dielectric relaxation observed at pure epoxy, for BTECF, there is the dielectric relaxation at 5-9GHz. It is mainly due to changing ofpolarization mode ofBTpowder itself In contrast, there is no relaxation for STECF up to 10GHz. Alternative materialfor embedded capacitorfabrication is epoxy/BT composite embedded capacitor pastes (ECPs). It uses similar materials formulation like ECFs and a screen printing methodforfilm coating. The screen printing method has the advantage offorming capacitor partially in desired area. But the screen printing makes surface irregularity during maskpeel-off Surfaceflatness is significantly improved by adding some additives and by applying pressure during curing. As a result, dielectric layer with improved thickness uniformity is successfully demonstrated. For 4X4 mm capacitors with 1] um thickness and 50 vol.% BT ECFs, dielectric constant of39, dielectric loss of 0. 023, capacitance density of2.6 nF/cm2, and 22% tolerance were obtained.

A primary factor of anisotropic conductive film (ACF) package failure is delamination between the chip and the adhesive at the edge of the chip. This delamination is mainly affected by the thermal shear strain at the edge of the chip. This shear strain was measured on various electronic ACF package specimens by micro-Moiré interferometry with a phase shifting method. In order to find the effect of moisture, the reliability performance of an adhesive flip-chip in the moisture environment was investigated. The failure modes were found to be interfacial delamination and bump/pad opening which may eventually lead to total loss of electrical contact. Different geometric size specimens in terms of interconnections were discussed in the context of the significance of mismatch in coefficient of moisture expansion (CME) between the adhesive and other components in the package, which induces hygroscopic swelling stress. The effect of moisture diffusion in the package and the CME mismatch were also evaluated by using the Moiré interferometry. From Moiré measurement results, we could also obtain the stress intensity factor K. Through an analysis of deformations induced by thermal and moisture environments, a damage model for an adhesive flip-chip package is proposed.Index Terms-Anisotropic conductive film (ACF), coefficient of moisture expansion (CME), delamination, electronic packaging, Moiré interferometry, reliability.

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