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Method for precut bump array film adhesive and preformed L-shaped film adhesive

IP.com Disclosure Number: IPCOM000033851D
Publication Date: 2004-Dec-30
Document File: 3 page(s) / 105K

Publishing Venue

The IP.com Prior Art Database

Abstract

Disclosed is a method for precut bump array film adhesive and preformed L-shaped film adhesive. Benefits include improved functionality and improved performance.

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Method for precut bump array film adhesive and preformed L-shaped film adhesive

Disclosed is a method for precut bump array film adhesive and preformed L-shaped film adhesive.  Benefits include improved functionality and improved performance.

Background

      Conventional capillary underfills (CUFs) produces uneven filleting, settling of filler, and flow difficulty for tight bump pitches that directly lead to package reliability issues (see Figure 1).

 

      Conventional technology uses the capillary effect to fill up the first-level interconnects with filler-rich epoxy. However, the use of the capillary effect produces difficulties as the bump pitch becomes increasingly smaller. The viscosity of the underfill material and the uneven distribution of fillers produce less acceptable results. Lower viscosity of the underfills can be used with less filler but with the expense of greater risk of thermal stressing failure. Lower viscosity underfills have a higher coefficient of thermal expansion (CTE) and lower modulus. These material properties result in increasingly stringent viscosity requirements for the first-level interconnects.

              Meeting the required control fillet angle is very difficult for conventional capillary underfills, especially at the tongue region. The high fillet angle increases the die stress along the die-side wall, which can cause die cracking.

      The conventional solution is to optimize the capillary underfilling process and carefully select the underfill material. This method may not be applicable to tighter bump pitches when the viscosity of underfills plays a significant role in ensuring even filler settling across the region. No fillet geometry control exists conventionally other than controlling the shot weight. High fillet angle continues to cause die cracking.

General description

      The disclosed method includes precut bump array film adhesive and preformed L-shaped film adhesive to improve the assembly process of  first-level interconnects and reduce die cracking. The L-shaped film adhesive material attaches to the perimeter of the die to couple the package, eliminating the concern of a nonuniform fillet angle. Die stress and die cracking are reduced and the consistency of producing a reliable product is increased.

      The precut bump array die film adhesive replaces the CUF process. The film adhesive is precut using a laser or other means to produce an array of precision holes for controlled collapse chip collect (C4) bumps. This film is optimized in thickness to be placed on the die and substrate prior to chip joining. The two pieces

adhere together while the bumps are formed during chip joining. For the filleting, four L-shape adhesive films are placed at each e...