SMTA International Conference Proceedings


Authors: Michael Peterson and Steven J. Adamson
Company: Belton Technology, Inc. and Asymtek
Date Published: 9/24/2006   Conference: SMTA International

Abstract: Hard Disk Drives (HDD) and products using System In Packages, (SiPs), like all other forms of consumer electronic (CE) devices, have to be small, lightweight and portable for convenience of the user. At the same time, new features and functions are being added to designs of HDD and SiPs that put tremendous pressure on the use of the substrate area. Flip chip (FC) devices and micro-BGA devices are being used as preamplifiers on flex circuits and substrates for these markets. Underfilling these devices on flex circuit and PCB substrate presents some fundamental problems for needles that Jet dispensing can eliminate.

Jetting overcomes the difficulties incurred on designs which are otherwise impractical to dispense with using a needle. An example of this is found in HDD Flex circuits and SiP packages, which have very high component density and little room to position a dispensing needle. Along with density concerns, flex circuits must be kept flat so as to support the design of receiving a FC. Stiffening layers are added to give the flex compliant system structure where an FC can be mounted. This rigid surface is also a requirement for establishing a known height from the substrate to needle tip, which is a critical control parameter in conventional dispensing. Jet dispensing on flex surfaces or on tightly designed SiP packages eliminates the need to precisely control the substrate to dispensing tip distance. As a result, Jetting can significantly increase throughput.

A process requirement of underfill is that it must be dispensed adjacent to the component edge, flip chip or micro-BGA, so that capillary forces pull the fluid under the device. At risk are other components near or in direct path of the dispense needle transfer pattern, which may become wetted with underfill and become contaminated with underfill. This creates concerns of wasting expensive underfill fluids or can lead to solder connections that do not meet proper IPC 610A criteria. A worse case is FC devices, which cannot be completely underfilled due to design densities and thus may be at risk of being starved of underfill at one corner of the device. In looking for solutions to these manufacturing challenges with dense packaging, Jet dispensing has proven very effective in being able to control the deposition of the underfill fluids and lower the risks associated with needle dispense transfer patterns. With the increased precision of dispensing position and jetting’s ability to take advantage of smaller substrate layout footprints, high layout densities are able to be achieved. Jetting is also able to significantly increase throughput as the need to slow down needle transfer speeds is no longer required with a jet.

The authors of this paper will discuss the merits of jetting verses needle dispensing. They will show how it has been possible to save board space while improving throughput in real life applications.

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