An investigation of tool wear in the dam-bar cutting of integrated circuit packages

doi:10.1016/S0043-1648(99)00350-6

Wear

Volume 237, Issue 2, February 2000, Pages 274-282

https://doi.org/10.1016/S0043-1648(99)00350-6 Get rights and content

Abstract

Dam-bar cutting is a mechanical trimming process in which the dam-bar between the leads of an integrated circuit (IC) package after post-molding process and deflashing is pieced out. Premature wear of the dam-bar cutting tool leads to higher operating costs and loss of production. In this paper, an investigation has been made to study the effects of punch–die clearance, leadframe materials, tool materials, tool coatings, punch shear and cutting speed on the wear of dam-bar cutting tools. The relationships between the punch flank wear, burr height and the dam-bar cutting force are also explored. Hence, critical factors are determined to optimize the tool life and improve the quality of the dam-bar cutting process.

Introduction

In the past, integrated circuit (IC) packaging was often considered as an auxiliary assembly process to silicon device fabrication and has received far less attention relative to its contribution to the overall device performance, reliability and cost [1]. However, the incessant drive toward high quality, high interconnection density, high lead counts, fine pitch, small size and thin packages pushes miniaturization of the packages to a stage where further miniaturization is constrained by the available packaging technology 2, 3. One of the major constraints in the development of packaging technology is on the design and the manufacture of sophisticated, high accuracy and high precision tooling for the IC trimming process. Apart from these, optimization of the tool life in IC trimming is also a crucial economical factor for minimizing the tool changeover time and preventing the production of unnoticed volume of defective devices. One of the IC trimming processes which is gaining great attention in the semiconductor industry is called dam-bar cutting (see Fig. 1). It is a process in which the dam-bars between the leads are pierced out after the postmolding and deflashing operations.

For high lead count and fine pitch packages such as 208 leads or even higher lead counts in Quad Flat Pack (QFP) packages, the dam-bars to be sheared are extremely small and delicate. The order of the sheared area and the thickness of the leadframe are usually less than one-tenth of a millimeter. In addition, the majority of the dam-bar cutting operations are now being done on high speed press. This demands for good wear and fatigue resistance of the tool material so as to maintain the dam-bar cutting quality over a longer service life before tool replenishment becomes necessary.

This paper discusses the effects of punch–die clearance, cutting speed, punch shear, leadframe materials, tool materials and tool coating on the wear of the dam-bar cutting tool. The relationships between the punch flank wear and the dam-bar cutting force were also analyzed under various percentage punch–die clearances and different leadframe materials. Hence, the critical factors that effectively reduce the amount of the dam-bar cutting tool wear will be identified for prolonging the tool life and the quality of the dam-bar cutting process.

Section snippets

Experimental details

The wear of the dam-bar cutting tool is such a complex phenomenon that there is no reliable general law for its solutions. This is probably due to the very large number of parameters which influence wear behaviour including the type and mode of loading, the frictional conditions of the contact surfaces between the cutting tool and the materials being cut, the interaction rate, the tool geometry and tool material properties, and properties of the materials being cut. In the present study, the

Effect of percentage punch–die clearance

The punch life curves, as shown in Fig. 4, suggest that a smaller punch–die clearance would result in a greater amount of flank wear. The useful life of the punch was also found to be reduced by about 33.3% as the clearance was decreased from 5.9% to 3.3%. SEM examinations of the cutting edge after 9000 cuttings (Fig. 5) indicated that a larger clearance would cause a comparatively smaller amount of wear at the cutting edge than a smaller clearance. The visible scratches with no macrochipping

Conclusions

An investigation of tool wear in dam-bar cutting of IC packages was carried out. Experimental results indicate that the amount of punch flank wear increases with increasing percentage punch–die clearance. Tools made of HSS exhibit the poorest wear resistance. The run-in wear at the cutting edge and the flank of the punch has proved to be substantially reduced by titanium nitride coating by PVD and surface treatment by plasma nitriding. Greater wear resistance was attained by plasma nitriding

Acknowledgements

The authors would like to express their sincere thanks for the research grants and technical supports provided by The Hong Kong Polytechnic University and ASM Assembly Automation Ltd., a public-listed manufacturer of semiconductor production equipment. They would also like to express gratitude to Mr. L.K. Chan, Mr. C.S. Chan and Dr. K.Y. Hung for their helpful advice and valuable support to the research project.

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An investigation of tool wear in the dam-bar cutting of integrated circuit packages

Abstract

Introduction

Section snippets

Experimental details

Effect of percentage punch–die clearance

Conclusions

Acknowledgements

Journal of Materials Processing Technology

International Journal of Machine Tool Design and Research

Journal of Electronic Packaging

Journal of Electronic Packaging

Journal of Engineering for Industry

Journal of the JSTP