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Method for a polishing head and a lapping technique for precision cross-sectioning and recovery of nonplanar ultra-thin die in SCSP and other BGA packages

IP.com Disclosure Number: IPCOM000010331D
Publication Date: 2002-Nov-20
Document File: 7 page(s) / 333K

Publishing Venue

The IP.com Prior Art Database

Abstract

Disclosed is a method for a polishing head and a lapping technique for the precision cross-sectioning and recovery of nonplanar ultra-thin die in stack chip scale packages (SCSPs) and other ball-grid array (BGA) packages. Benefits include improved functionality and improved ease of manufacturing.

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Method for a polishing head and a lapping technique for precision cross-sectioning and recovery of nonplanar ultra-thin die in SCSP and other BGA packages

Disclosed is a method for a polishing head and a lapping technique for the precision cross-sectioning and recovery of nonplanar ultra-thin die in stack chip scale packages (SCSPs) and other ball-grid array (BGA) packages. Benefits include improved functionality and improved ease of manufacturing.

Background

        � � � � � The conventional trend in flash memory packaging technology is to stack as many dice as possible in very-thin BGA packages, such as SCSP and folded SCSP, which necessitate significant thinning of the die to maximize the stack. Conventional BGA packages with stacked-up ultra-thin dice fail some percentage due to random failure modes, such as memory array and parametric failures in any of the dice in the stack.�

        � � � � � Results of failure analyses indicate that the cause of some of the failures is related to the stacking of the dice. However, the most common cause is foreign particles in adhesive die attach and in the passivation layers. The placements of the dice in the package are not always planar and sometimes create a major problem during the process of recovering the failed die. Even an expensive precision polishing machine with a perfectly planar polishing head relationship to the polishing wheel is ineffective when it cannot compensate for nonplanar dice in the stack. The result can cause damage to the die being recovered. Sometimes the defects that cause failures are lodged in the die-to-die adhesive interface. These defects are easily lost during the polishing process, due to accidental over polishing when some of the dice in the stack are nonplanar.

        � � � � � In the case of folded SCSPs, a very expensive laser-milling machine is used to recover the dice. However, the use of this machine cannot guarantee full functionality. The unit still requires a hard to control, unsafe, and inconsistent eyedropper method of acid etch. Sample preparation, such as mounting the unit onto the polishing chuck using adhesive wax, if not properly done, can contribute to nonplanar sample mounting. It can result in accidental destruction during the polishing process.

General description

        � � � � � The disclosed method is a polishing head and a lapping technique for planarizing nonplanar dice in BGA packages during the recovery of a failed die. The polishing head compensates for nonplanar dice and adapts a newly designed cross-sectioning stub/sample holder, which adds a precision cross-sectioning feature to the polisher.

Advantages

        � � � � � The disclosed method provides advantages, including:

•        � � � � Improved functionality due to the improved capability for the goniometer to be adjusted, positioned, and calibrated

•        � � � � Improved ease of manufacturing due to the improved eased of planarization, polishing, and cross-sectioning

•        � � � � Improved cost effectiveness due to the disco...