Excimer Laser Applications in Integrated Circuit Packaging
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ABSTRACT Excimer laser ablation is applied in the deflashing and demarking of IC packages. It is found that mold flash filled in the interface holes of IC leadframe can be removed completely by the laser deflashing in a short period of time. With appropriate selection of laser parameters, deflashing quality and efficiency can be greatly improved. The laser deflashing is more efficient for higher pin count packages. It is a superior alternative in future applications. In laser demarking, ink marks on package surfaces can also be removed completely in a short time. The surface after the processing has good conditions for remarking. The package remarking shows good permanency. The lifetime for good marking is much longer for IC packages after the laser demarking than those after hydrogen flame-off Laser processing can be used to replace hydrogen flame-off in the ink printing of IC packages for high efficiency and safety.
INTRODUCTION With its wavelength in UV spectrum and pulse duration in an order of nanoseconds, excimer laser ablation has been widely used in material processing. In this article, its applications in the deflashing and demarking of IC packages are reported. In IC packaging, mold flash usually fills the interface holes of IC leadframe. It must be removed during manufacturing[I]. Mechanical punching, water-jet sputtering and chemical deflashing are commonly used in the industry[2]. However, these methods cannot remove the flash completely and require subsequent processes[3]. As IC technology develops, pin count in an IC package becomes higher and interface holes become smaller. This makes it more difficult for the conventional methods to remove mold flash completely. Based on the laser ablation of mold materials, the excimer laser deflashing can remove mold flash completely. This process has the advantages of being dry, non-contact, easily controllable and highly efficient, and may be a suitable option in future applications[4]. In the industry, manufacturers often meet some inevitable cases, such as wrong or poor marking of the packages and suddenly changing some specific designation for customers. To discard an acceptable device at this backend step will make IC yield drop and raise the device cost. The practical way is to remark the device[5,6]. Typically, packages to be remarked have existing marks on package surfaces. Conventional techniques to remove prior markings include manual scrubbing and propelling abrasive particles at high speed. However, these methods have many drawbacks, such as low speed, less automation and rough surfaces after the processing. This limits their applications in the device manufacturing[5]. In this article, excimer laser processing is introduced to remove ink marks on package surfaces.
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Mat. Res. Soc. Symp. Proc. Vol. 397 0 1996 Materials Research Society
EXPERIMENT In the experimental setup for excimer laser applications in IC packaging, a KrF excimer laser (Lambda Physik LPX 100) is used as the light source. The laser beam has a wavelength of 248 nm -and a puls
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