SMTA International Conference Proceedings


Authors: Renn Chan Ooi, Cheng Siew Tay, Alan C McAllister, Karissa J Blue, and Lian Huat Ng
Company: Intel Product (M) Sdn. Bhd.
Date Published: 10/11/2007   Conference: SMTA International

Abstract: The use of board level adhesives in electronic packages to enhance mechanical solder joint reliability (SJR) has long existed in the industry. Handheld industry uses full underfill solution on small BGA packages to withstand free drop use condition while corner glues are common solutions in laptop products which are using larger BGA packages. Despite the long history of board level adhesive application in the industry, limited studies were performed to identify the cost effective solution for each application especially in the new application like ultramobile personal computer (UMPC).

The first part of study focused on the effectiveness of different categories board level adhesive technology with respect to the mechanical shock protection, ease of manufacturability (reworkability, processing time) and cost. The second part of study was designed to identify key attributes for optimized adhesive geometry. The objective of the paper is to provide industry a technical guideline in selecting cost effective adhesive solution for various electronic applications.

Three categories of board level adhesive technology evaluated are full underfill (FF), partial underfill at package corner (CF) and corner glue (CG). Assembled packages with adhesive were evaluated using increasing shock acceleration levels until electrical failures were detected. These shock levels are used as performance indicator of each adhesive solution. Shock data indicated FF and CG have high performance as compared to CF. CG appears to be a more cost effective solution than FF with consideration of material consumption and ease of reworkability. Thus, the subsequent studies were done on the CG. Shock models constructed using Finite Element Method (FEM) with varying CG geometric attributes were used to predict their respective effect towards CG stresses. CG dispensing process was controlled to produce similar geometries as simulated in FEM for empirical validation. In this refined study, optimal CG fillet geometry was defined in terms of fillet height, width and coverage depth. The importance of CG fillet geometry to SJR performance is as critical as CG material selection. This highlights the importance in assembly process control to achieve optimum CG fillet geometry.

Key words: corner glue, underfill, adhesive, shock, BGA

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