SMTA International Conference Proceedings


JET DISPENSING UNDERFILLS FOR STACKED DIE APPLICATIONS

Author: Steven J. Adamson
Company: Asymtek
Date Published: 9/26/2004   Conference: SMTA International


Abstract: It is not uncommon to see three to five layers of silicon in stacked die packages. By going vertical, designers get greater utilization of the board space and can implement mixed silicon technologies, such as memory and microprocessor technology. Stacked packages often use combinations of flip chip and wire bonded die. When a flip chip is used as one of the layers of the stack, dispensing space is often tight, with limitations on the area where underfill fluids can be dispensed. Any time a needle has to be positioned accurately in a restricted space between a die and wire bonds, the process can run slow. Jet dispensing of underfill overcomes this limitation by shooting dots from a safe height above the flip chip and wire bonds. The lower tolerance positioning requirements for jet dispensing leads to higher throughputs.

This paper will review the state of dispensing for stacked die applications and contrast jetting technology with needle dispensing. It will also offer guidelines for layout rules for Printed Circuit Boards / packages designed to utilize the benefits of jetting technology.

For the last twenty years, dispensing has evolved from pushing fluid through a needle using air pressure, to a highly automated production process with linear positive dispensing pumps and now: jetting. Controlling fluid deposition, needle position and dispensed volume accuracy has dramatically improved in recent years.

Additionally, speed has increased while software has simplified operational control. Jetting underfills and encapsulants is now practical, and it is having a large impact on the electronics assembly.



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