Pan Pacific Symposium Conference Proceedings


Authors: Hsiang-Chen Hsu, Ming-Kun Chen, Yu-Jung Huang, and Shen-Li Fu
Company: Department of Electrical Engineering, I-Shou University
Date Published: 1/24/2008   Conference: Pan Pacific Symposium

Abstract: In this paper, experimental approaches to analyze failure site conditions for the final testing of ball grid array (BGA) packages are described. Findings of touchdown times-related changes in BGA socket are presented. The electrical characteristics of the individual chips on BGA packages are generally tested using a BGA socket of the pogo pin type. To ensure the accuracy of the measurement results, it is essential that a low and stable contact resistance is maintained between the pogo pin and the solder ball of the BGA packages. In conventional final testing of BGA package, the BGA sockets are punctured against the solder ball to obtain a low contact resistance by mechanically breaking down the interfacial oxide layer on the solder ball.

When testing BGA packages using a pogo pin socket, maintaining a low contact resistance and a stable contact characteristic is fundamental function. However, the electrical contact between the crown of pogo pin and the solder ball of BGA package becomes unstable following repeated contacting operations since particles from the substrate edge gradually accumulate on the crown of pogo pin. The contamination caused by these particles causes the contact resistance and the unstable contact characteristic to increase. These may impact system performance as a result of time-based discontinuities, where a momentary high resistance or open circuit causes data transmission errors during final testing. This paper provides an experimental procedure for investigating the effect of particle contamination and the worn-out of crown tip. The surface conditions were observed by optical microscope (OM), scanning electronic microscope (SEM), and energy dispersive X-ray spectrometry (EDX) techniques after the final testing operation. The experiment is conducted to investigate the accumulation of surface particles on the crown tip following multiple contacts with the surface of solder ball for production devices. The extent of worn-out tips following 6,830, 13,630, 20,000, 27550 and 36,580 touchdowns, respectively. The contact resistance of the used pogo pins is then measured at compacted condition. The experimental results the surface analysis of crown tip and socket base and compares with a bismaleimide triazine (BT) layer of substrate, a punch surface of substrate and a socket surface are observed. The contact resistance experiment conducted using a clean BeCu/Au plated pin indicate that the contact resistance and the variable value increase with an increasing number of touchdowns.

Key words: BGA socket, optical microscope (OM), scanning electronic microscope (SEM), energy dispersive X-ray spectrometry (EDX)

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