Flexibility for Semiconductor Prototyping

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Process development can present many challenges in the die attach market when the optimal process or package design varies drastically. Specifically, the interconnect methods can include conductive epoxy, solder paste, sintered paste, eutectic preforms, wire bonding, flip-chip with ball bumps, etc., which all require different technologies and equipment. Understanding which interconnect method is best for a particular application is not an easy or quick task. Process development and design optimization can span years, and yet it is vital to staying competitive in today’s continually evolving technological world.

It is essential to have flexibility in the technologies available for prototyping and developing new designs. The challenge with many technologies used for high volume production of various interconnect strategies is that they are specialized and expensive. It is simply not feasible to purchase capital equipment to test every new design as optimizations become apparent.

Palomar’s Innovation Center offers a wide variety of equipment for prototyping and process development. Process engineers work closely with customers through the process development and product prototyping phases, while simultaneously assisting them in determining the best equipment to use for the high volume manufacturing of their newly improved design.

Case Study: Improving Assembly Processes for High Powered LED Attachment

Palomar’s Innovation Center has been working with a customer developing an LED assembly for the past few years.  Their original packaging assembly required dispensing a very fine amount of silver sintered paste to attach tens of LEDs to a customized aluminum substrate. With a focus on thermal conductivity to maintain the longevity of the LEDs, a process was developed using the Palomar 3880 Die Bonder equipped with a dispensing system. The Palomar 3880 accurately and quickly dispensed the paste and placed the LEDs onto the assembly before transferring them to an oven to finalize the process. Innovation Center engineers continued to work with the customer to improve the package design, assembly procedures, and material selection over the next few years. Specifically, Palomar helped facilitate a transition from a customized aluminum substrate to a mainstream MCPPCB, helping reduce costs.

Recently, however, the customer wanted to significantly enhance the lifetime of their LEDs on the assembly by exploring vastly different interconnection methods. The primary goal was to maximize the thermal conductivity of the bond between the substrate and the LEDs to get as much heat away from the high powered devices and out of the package as possible.  Palomar worked closely with the customer to test multiple attachment methods for their new package before settling on a robust process using AuSn preforms and the SST 5100 - a vacuum reflow system, in addition to the existing Palomar 3880. 

This new process entailed using the Palomar 3880 to first dispense a specially formulated fluid onto each bonding surface which worked to hold accurately placed preforms and the LEDs in place to be transferred for a batch reflow in the SST 5100. Tight volume control during dispensing was necessary to ensure the components were tacked sufficiently while simultaneously keeping the fluid at a minimum to prevent the components from drifting. The SST 5100 provided a unique combination of positive and negative pressures during the reflow cycle which ensured near zero voiding in the bonds for each device. 

This solution provided a significant improvement to the longevity of the LEDs while maintaining high throughput and quality of the assemblies. Not only was the unique combination of equipment vital to this successful process design, but it also allowed the customer to iterate between several package designs and processes by using a total solution provided by Palomar’s Innovation Center.