Medical Electronics Symposium Conference Proceedings


Author: Todd Woods / Steven J. Adamson
Company: Plexus Corporation / Asymtek
Date Published: 5/19/2004   Conference: Medical Electronics Symposium

Abstract: Medical devices that have to be implanted in humans need to be as small as possible to avoid discomfort to the user. At the same time new features and functions are being added to these devices which increase the difficulty of minimizing their overall size. In addition, components such as flip chip and CSP, typically found on medical devices, require underfill which further complicates the need for space minimization.

Medical devices that use these types of area array components have common problems. The use of a large variety of device types and the limited real estate that underfill materials can be applied causes iterative development. Figure 1 shows the variety of device types that can be encountered on a single assembly. To improve board utilization Plexus investigated options to dispense underfills for medical devices.

In a number of applications, underfill materials are not allowed to contact die surfaces due to active backside operation, adjacent wire bonds or components. This has put pressure on dispensing companies to develop techniques for creating small fillets of underfill or encapsulants in a controlled manner. Precision movement of a dispensing needle tip usually involves slowing the speed of the dispense head down so small needles can maneuver into position and dispense in tight spaces, reducing throughput times. There are additional limits to how small of a needle can be used. Jet dispensing overcomes these barriers to enable assembly designers to obtain compact designs.

The goal of this paper is twofold. It will describe the work done to develop a jet capable of dispensing underfill materials and one that produces smaller fillets and controlled dispensing. Secondly, it presents an example of how jetting was used in the assembly of medical devices which utilized flip chip technology with fillet length limitations due to space constraints.

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