SMTA International Conference Proceedings


Author: Dr. Paul P.E. Wang
Company: Sun Microsystems
Date Published: 9/22/2002   Conference: SMTA International

Abstract: The technical challenges of reworking close packed high density I/O BGA components has long been on the critical path for further increasing the layout density of Printed Circuit Board designs. As an initiative to overcoming this challenge, a series of controlled studies will be conducted to evaluate the machine capability and feasibility of laser rework on various packages and thicker (0.125") PCB fabrication technologies.

This article will explore the new developments in Laser Rework Technology and its correlation to the reliability of high density I/O FCBGA on a custom test vehicle. Comprehensive Design of Experiments (DOEs) will be used to build the basis for an optimal manufacturing process encompassing solder paste printing, thermal operations performed to the package and other related manufacturing assembly.

Test vehicles assembled under these conditions will then be subjected to the laser rework. Highly Accelerated Life Testing (HALT) will be performed to establish the reliability correlation to the process and used as a response for the final statistic analysis. Analytical methods such as Shadow Moiré, IST, 5DX, Laser Scan, SEM, EDX, XRF, TDR, SVS, and AOI are extensively used to screen incoming quality of packages and PCB fabrication to derive an acceptable process window for assembly of the test vehicles.

Laser rework equipment features such as mechanical placement, vision alignment, ramp rate and thermal uniformity of a newest generation Laser Rework Machine will be evaluated. Component clearance of packages under laser rework will be examined and criteria proposed.

Absorptivity differential of the package due to color and surface finish will be correlated to the reliability and fracture mechanism of the solder joint produced by the optimal manufacturing process.

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