Automated backside polishing bonniegannon5 08

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EDFAAO (2008) 2:6-10

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Backside Polishing Technique

Automated Backside Silicon Polishing for Die Encapsulated in a Package Bonnie Gannon, IBM Systems and Technology Group, Essex Junction, Vt. blgannon@us.ibm.com

Introduction With the growing complexity of new processes and packaging material, the need for automated backside silicon polishing for integrated circuits (ICs) is necessary. The ability to achieve successful polishing results in cases where ICs are mounted on ceramic or laminate material is not as difficult because the ICs are above the substrate. For ICs encapsulated inside packaging material, it is more challenging to obtain a scratch-free silicon surface.

procedure is followed with 30, 15, 6, 3, and finally 1 μm diamond paste steps. This process could possibly take 2 to 3 h to complete. There are many inherent problems with this process. It can be rather difficult to master the technique of pressing hard enough on the silicon surface to remove the scratches and, at the same time, pressing gently enough so as not to cause uneven surface topography.

There are a variety of tools to perform fault localization tests for microelectronics failure analysis. These techniques often require the silicon to be thinned and optically polished to acquire unobstructed signals from the circuits from the backside. The previous method required an operator to hand polish the ICs for testing. A newly improved automated process for polishing the surface of the silicon offers many advantages.

Previous Sample Preparation Method

Fig. 1

Surface topography line scan results

Fig. 2

Edge scratches after hand polishing

When it has been determined that a particular sample has a defect, the lid or packaging material is removed above the silicon using a high-precision milling tool with an end mill. The epoxy is then scraped off the silicon with a razor blade to expose the backside surface. The IC is thinned to the appropriate thickness with a diamond bit, which leaves a silicon surface roughness of approximately 1200 nm (Fig. 1). The sample is removed from the tool, and hand polishing begins. A cotton tip is inserted into a rotary tool to facilitate the application of a variety of diamond pastes to attain a smooth surface. Typically, a 45 μm paste is applied with a lubricant until the scratches from the diamond bit have been removed. This

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Electronic Device Failure Analysis


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