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The purpose of this paper is to provide a design and material selection guideline for a plastic ball grid array (PBGA) package in order to improve its reliability and manufacturing ability after post mold cure.

Numerical experiments based on a three‐dimensional (3‐D) viscoelastic finite element method have been conducted to evaluate governing damage mechanisms after post mold cure (PMC) for PBGA packages. The parametric studies for the PBGA package with various molding compounds have been performed. A wide range of the modulus (1MPa∼15GPa) and the coefficient of thermal expansion (CTE) (10ppm∼300ppm) are evaluated to see feasibility of a new class of material set in the molding compound. Effects of thermo‐mechanical properties of selected molding compound on the warpage and residual stress of the PBGA are analyzed.

The present study shows that the material properties such as modulus and CTE of molding compounds play an important role in warpages and reliability of PBGA packages. After post mold cure, compressive normal stress σ_xx is observed in the silicon die, while tensile stress occurs in the rest of the PBGA package. The maximum normal stress σ_xx is observed at the center of the silicon die and decreases near the edge of the package. As the coefficient of thermal expansion of the silicon die is substantially less than that of the molding compound or substrate, the molding compound and the substrate are trying to shrink more when temperature decreases and in turn compressing the silicon chip. The molding compound with low modulus produces low stresses in the Si die and the die attach. Moreover, for the low modulus case, the CTE of molding compound does not affect the warpage of the PBGA package and the stresses in the silicon die or the die attach. However, for the high modulus case, the warpage and stresses are increased significantly by increasing the CTE of molding compound.

It is suggested that adhesion strengths of die attaches should be studied in future studies, since those affect the delamination between dies and substrates.

The findings can be used as general design guidelines for a PBGA package.

The results presented in the paper will be very useful to designers of PBGAs.

The purpose of this paper is to investigate the thermomechanical response of four well-known lead-free die attach materials: sintered silver, sintered nano-copper particles, gold-tin solders and silver-tin transient liquid phase (TLP) bonds.

This examination is conducted through finite element analysis. The mechanical properties of all die attach systems, including elastic and Anand creep parameters, are obtained from relevant literature and incorporated into the numerical analysis. Consequently, the bond stress-strain relationships, stored inelastic strain energies and equivalent plastic strains are thoroughly examined.

The results indicate that silver-tin TLP bonds are prone to exhibiting higher inelastic strain energy densities, while sintered silver and copper interconnects tend to possess higher levels of plastic strains and deformations. This suggests a higher susceptibility to damage in these metallic die attachments. On the other hand, the more expensive gold-based solders exhibit lower inelastic strain energy densities and plastic strains, implying an improved fatigue performance compared to other bonding configurations.

The utilization of different metallic material systems as die attachments in power electronics necessitates a comprehensive understanding of their thermomechanical behavior. Therefore, the results of the present paper can be useful in the die attach material selection in power electronics.

The trend towards higher density, higher frequency, higher power active devices in placing increasingly difficult demands on device packaging. Materials with high thermal conductivities are replacing the traditional ceramics in hermetic, high power packages, and MCM/ hybrid modules. Thermally enhanced plastic packages more frequently feature heat sinks embedded in the package for direct attachment of the power devices. Today's challenge in electronic packaging is to dissipate the heat from the source, the device itself, without affecting its electrical performance or reliability. The material directly contacting the device is the die attach medium. On lower power packages, the die bond line is not usually the highest thermal resistance in the thermal path. With highly conductive substrates and heat sinks, the die attach material now becomes the critical element directly in series with the highly conductive substrate. Fundamental limitations in thermal properties of about 3 W/mK exist in present‐day organic adhesives, primarily of the thermosetting type. This thermal conductivity (k) does not meet the current demands of thermally enhanced plastic laminate packages, MCMs, or direct die attach to heat spreaders or heat sinks. This paper describes the development, properties and application of electrically conductive thermoplastic adhesive pastes having thermal conductivity values as high as 35 W/mK, and able to produce thin, void‐free bond lines for maximum thermal transfer. The key material variables are isolated and evaluated for their impact of the k value. DOEs (design of experiments) were run to optimise the combination of the key variables, namely size/shape of the filler and the volume fraction to produce the highest k without sacrificing other functional properties such as adhesion. The effect of polymer chemistry (thermoset and thermoplastic) was also studied. The properties of the newly developed, enhanced conductivity thermoplastic adhesives are compared with other material technologies and examples of current applications reviewed.

The purpose of this paper is to design a novel die-attach composite joint for high-temperature die-attach applications based on transient liquid phase bonding. Moreover, the microstructure, shear strength, electrical property, thermal conductivity and aging property of the composite joint were investigated.

The composite joint was made of microporous copper and Cu₃Sn. Microporous copper was immersed into liquid Sn to achieve Sn-microporous copper composite structure for die attachment. By the thermo-compression bonding, the Cu₃Sn-microporous copper composite joint with a thickness of 100 µm was successfully obtained after bonding at 350 °C for 5 min under a low pressure of 0.6 MPa.

After thermo-compression bonding, the resulting interconnection could withstand a high temperature of at most 676 °C, with the entire Sn transforming into Cu₃Sn with high remelting temperatures. A large shear strength could be achieved with the Cu₃Sn-microporous copper in the interconnections. The formed bondlines demonstrated a good electrical and thermal conductivity owing to the large existing amount of copper in the interconnections. Furthermore, the interconnection also exhibited excellent reliability under high temperature aging at 300 °C.

This die-attach composite joint was suitable for power devices operating under high temperatures or other harsh environments.

Due to oxide formation at the die backside, excessive non‐wetting and voiding can occur especially for the larger die (100K sq. mil) by gold eutectic die attach. Such voiding can cause die lift‐off and cracking. Ag/glass seems to be a promising candidate. However, it has some shortcomings. First, solder seal hermeticity reject may occur due to nickel diffusing through gold metallisation and being oxidised on the surface of the multilayer package. Secondly, for those devices requiring backside contact, gold metallisation on the die backside becomes the barrier for the reaction between the silicon and the glass. The adhesion may be degraded. The factors which may overcome these shortcomings will be discussed.

For a considerable time moisture level has been a problem for hermetic package assembly, although the materials used were only metallics. Today semiconductor technology is cost driven, therefore organic materials must be taken into account. Obviously there are many different issues involved. This paper focuses on mechanisms involving hermetic packages with silver glass die attach material. Silver glass, as a die attach paste, is mixed with organic solvents, so different chemical reactions are studied. It is then shown how to achieve a low moisture level. the authors' company has performed a design of experiments (DoX) in order to identify the key parameters and their interactions. A mathematical prediction model has been determined, and the result of this theoretical study is confirmed with experimental results.

Several commercially available epoxy and polyimide adhesives were tested. The properties essential for the use of adhesives in microelectronics are stated and their compliance with the requirements of standard MIL‐A‐87‐172 was evaluated.

The challenge presented by advanced package development in the past five years has further accentuated the constant need for package quality and reliability monitoring through extensive laboratory testing and evaluation. As pin counts and chip geometries have continued to increase, there has been additional pressure from the military and commercial sectors to improve interconnect designs for packaged chips, including chips directly attached to the printed wiring board (PWB). One of the options employed has been tape automated bonding (TAB). However, this assembly technique also presents new standardisation, qualification and reliability problems. Therefore, at Rome Air Development Center (RADC), there is regular assessment (through in‐house failure analysis studies) of parts destined for military and space systems. In addition, Department of Defense (DoD) high tech development programmes, such as very high speed integrated circuits (VHSIC), have utilised all present screening methods for package evaluation, and have addressed the need for development of more definitive non‐destructive tests. To answer this need, two RADC contractual efforts were awarded on laser thermal and ultrasonic inspection techniques. Through these package evaluations, a number of potential reliability problems are identified and the results provided to the specific contractors for corrective action implementation. Typical problems uncovered are lid material and pin corrosion, damage to external components and adhesion problems between copper leads and polyimide supports, hermeticity failures, high moisture content in sealed packages and particle impact noise detection (PIND) test failures (internal particles). Further tests uncover bond strength failures, bond placement irregularities, voids in die attach material (potential heat dissipation problems), and die surface defects such as scratches and cracks. This presentation will review the specific package level physical test methods that are employed as a means of evaluating reliable package performance. Many of the tests, especially the environmental tests—e.g., salt atmosphere and moisture resistance—provide accelerated forms of anticipated conditions and are therefore applied as destructive tests to assess package quality and reliability in field use. In addition to a manufacturer's compliance with designated qualification procedures, the key to package quality lies in utilising good materials and well‐controlled assembly techniques. This practice, along with effective package screen tests, will ensure reliable operation of very large scale integration (VLSI) devices in severe military and commercial environment applications.