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This paper aims to analyze the effect of surface roughness and hardness of leadframe on the bondability of gold (Au) wedge bond using in situ inspection of laser interferometer and its relationship with the deformation and wire pull strength.

The in situ inspection of ultrasonic vibration waveform through the changes of vertical axis (y-axis) amplitude of wire bonder capillary was carried out using laser interferometer to analyze the formation of Au wedge bond. The relationship between the changes of ultrasonic waveform of capillary with the deformation and the pull strength was analyzed to evaluate the bondability of Au wedge bonds.

It was observed that the changes in vertical axis amplitude of ultrasonic vibration waveform of wire bonder capillary can be used to describe the process of bonding formation. The loss of ultrasonic energy was exhibited in ultrasonic vibration waveform of wire bonding on leadframe that has higher value of roughness (leadframe A) as compared to that of leadframe that has lower value of roughness (leadframe B). The lower pull strength obtained by Au wedge bond further confirms the reduction of bond formation because of the higher deformation on leadframe A as compared to that of leadframe B.

The relationship between in situ measurement using laser interferometer with the bondability or deformation and wire pull strength of Au wedge bonds on different surface roughness and hardness of leadframes is still lacking. These findings provide a valuable data in analyzing the bonding mechanisms that can be identified based on the in situ measurement of ultrasonic vibration and the bondability of Au wedge bonds.

The purpose of this paper is to determine the key process factors which affect the adhesion strength of encapsulation molding compounds (EMCs) to leadframes to obtain reliable components without any need to pretreat the leadframe surface.

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°C provides the largest process window. Leadframe oxidation can increase adhesion first, but then decrease it drastically with further oxidation. The powder moisture content has mixed effect on adhesion.

By molding at 175°C, limiting the wire bonding time and minimizing the powder moisture content, reliable components can be obtained without any need for leadframe surface pretreatment such as plasma cleaning or surface coating.

Quantify the key process factors which affect the adhesion of EMCs and reveal reason behind the current industrial practice of using the mold temperature of 175°C.

To demonstrate thermal modeling technique for a through hole light emitting diode (LED) package using a commercial computational fluid dynamic (CFD) code and to improve its thermal performance through a series of sensitivity analyses.

Thermal resistance of the standard through hole LED is calculated using the simulation result. The result is then compared with actual measurement to establish the correct model. Using the validated model, series of sensitivity analyses are carried out through simulation. Taking the most optimum design, a prototype of the improved LED is fabricated and the thermal resistance performance is compared with the simulation result.

The simulation result of the standard LED is close to actual measurement with 5 percent difference. The thermal resistance of the through hole LED is reduced by changing the leadframe material from mild steel to copper alloy and increasing the leadframe width. Combination of both design changes resulted in thermal resistance reduction of 51 percent.

This paper identified the practicality of using CFD codes in achieving fast and accurate result in thermal modeling of LED package and also offers solutions on reducing the LED thermal resistance.

This paper explores the enabling technologies and thermal performance trade‐offs associated with inserting small multichip modules (MCMs) into surface mount packages. Using assembly and interconnect technologies available today, ‘few‐chip’ packages can lead to less costly solutions than traditional single chip package approaches, and may be practical depending on system size and modularity constraints. The key enabling technologies required include fine‐line interconnect substrate technology, direct leadframe attachment and chip bonding to fine‐line laminate substrates, the moulding of large substrates with multiple components in a thin surface mount package, and cost‐effective cooling techniques. The thermal performance of a moulded few‐chip package is analysed and cooling methods are discussed. A screening experiment was performed in which several geometric and material parameters were studied to determine their impact on thermal performance. The size of the heat slugs appears to be the variable with the greatest effect on thermal performance. The effects of external board size, board material and the design of the internal substrate on the thermal performance of a few‐chip packaqe are also discussed.

In Part 1, background information on mechanical properties and metallurgy of solder alloys and soldered joints has been presented. In Part 2, mechanisms of damage and degradation of components and soldered joints during soldering, transport and field life have been discussed, the most important mechanism being low cycle fatigue of the solder metal. In this third part, the determination of the fatigue life expectancy of soldered joints is discussed. Accelerated testing of fatigue is needed, as the possibilities of calculations are strongly limited. A temperature cycle test under specified conditions is proposed as a standard. A model is worked out for the determination of the acceleration factor of this test. A compilation of a number of solder fatigue test results, generated in the author's company, is presented.

Wire bonding is an important method of interconnection in microelectronics. Ultrasonic energy is known to soften metallic materials and hence when used in the wire bond process it is effective to decrease the flow stress similar to thermal energy. The paper aims to address this issue.

Detailed resonance studies show that some designs have closeby resonance compared to the bonding frequency which causes enhanced vibration resulting in such over squashed bonds. Hence, precautions in the design stage are necessary to understand the closeby resonance frequencies and corresponding mode shapes of the leadframe that are in‐plane in nature along the transducer axis that can be excited by the capillary's motion. This can be determined a priori using numerical methods such as finite element method. In this paper, one such case study has been dealt in detail to explain the overall methodology.

To minimize the effects of resonance, damping should be increased by bonding polyimide tapes to enhance damping and stiffness which results in better ball bonds with optimum bell shape.

The paper explains the methodology of wire bonding in microelectronics.

There is a reliability concern in the larger plastic surface mounting packages which can exhibit cracks from internal stresses during soldering. A lot of ad hoc information has been given to users of such packages about the origins of the problem and its alleviation. The phenomenon is the result of a combination of moisture absorbed in the plastic and the thermal stresses caused by the different expansions of the metal leadframe and the plastic. The work reported here gives quantitative data regarding the amount of moisture absorption critical to cracking, the range of baking procedures available to reduce this moisture below the critical level, and the acceptable floor life after baking for a wide range of storage temperatures and humidities.

Palladium surface finishes are utilized on leadframes, printed wiring boards and automobile sensors. Their superior functional performance and the considerable environmental impact of plating lead‐free finishes for packaging processes have been increasingly recognized by the electronic industry. Wire bondable and solderable palladium finishes meet military and industrial standards at no extra cost in the overall assembly processes when compared to traditional packaging techniques. In addition to the development of palladium plating chemistries and technologies, the functional properties of the surface finishes including their wire bonding performance have also been investigated at Bell Laboratories. In this study, gold and aluminum wire bonding to palladium finishes was tested and the wire bond pull force and break position were examined in order to optimize the bonding processes. The results of the study are reported in this paper.

In Part 1, background information on mechanical properties and metallurgy of solder alloys and soldered joints has been presented. In this part, mechanisms of damage and degradation of components and soldered joints during soldering, during transport, and during field life are discussed. Thermal shock damage of components and excessive dissolution of metallisations are the major effects during soldering. During transport, fatigue of leads and fracture may be caused by vibration and mechanical shocks respectively. During field life, degradation is governed primarily by low cycle fatigue of the solder and incidentally also by formation of intermetallic diffusion layers between solder and base metals. This article contains an extended illustration of solder fatigue of joints on a variety of component and board types. Finally, the influence of the variety of soldered constructions in electronic circuits on solder fatigue is discussed.