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Method for a cool capillary underfill dispense process

IP.com Disclosure Number: IPCOM000008753D
Publication Date: 2002-Jul-09
Document File: 3 page(s) / 92K

Publishing Venue

The IP.com Prior Art Database

Abstract

Disclosed is a method for a cool capillary underfill dispense process. Benefits include improved process quality and improved throughput.

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Method for a cool capillary underfill dispense process

Disclosed is a method for a cool capillary underfill dispense process. Benefits include improved

process quality and improved throughput.

Background

              The conventional C4 epoxy underfill process uses capillary action to both underfill the die and to produce fillets on the sides of the die. Due to lowered epoxy viscosities at higher temperatures, the speed and quality of this capillary action is highly dependent on temperature. Improper average temperature and nonuniformities can result in poor adhesion of the underfill to the die and/or to the package as well as forming voids in the underfill. Voids increase the risk for bump shorts and opens through repeated thermal-mechanical stressing. The strong dependence on temperature is increasing with packaging technology trends, including trends toward lower gap heights between the die and the package, decreased C4 bump pitch, and increased die sizes.

              The conventional process of record (POR) is highly dependant on temperature control. Part temperatures are maintained within a relatively narrow spread throughout the dispensing process (see Figures 1-3). After a carrier arrives at the dispensing station, it moves through a series of heating stations:

1.      Preheating prior to the first dispense

2.      Heating during the first dispense

3.      Preheating prior to a second dispense

4.      Heating during the second dispense

              At each of these stations, a large impingement heater is raised to close proximity with the underside of the carrier. This arrangement maintains part temperatures at or near to the optimum temperature that minimizes issues with the quality of the underfill and fillets.

              The rise in ambient temperature in the dispenser, coupled with the change in epoxy material properties due to continued exposure to high temperatures, produces several disadvantageous side effects. The effective process window is greatly reduced. Part-to-part variation in quality is high. Unit-leve...