"Borrowed" Prototyping System Solves Major Semiconductor Test Problems

Circuit board plotter for engineering prototypes yields big dividends in the test department

Introduction: Test Engineers at Supertex Inc have been "borrowing" an LPKF ProtoMat® circuit board plotter system to solve some of their most difficult testing problems. Applications Engineers brought in the plotter to produce prototype boards that are used to demonstrate the company’s new high-voltage integrated circuits. The plotter is now being used to fabricate hundreds of test fixtures as well, yielding big dividends in turnaround time, lower test costs and improved accuracy of test results.

The Problem: Unreliable test fixtures cause downtime, errors

Testing is a vital part of semiconductor development and test fixtures are the proverbial "horseshoe nails" that make or break measurement results. Inadequate or unreliable test fixtures were causing major disruptions to new product introductions at Supertex due to mechanical failures and improper test results.

Frank Galica, Hardware Engineer/Supervisor, explained, "We were building typical generic wire wrap fixtures to adapt our new devices to the dozens of test stations we maintain. The connectors on the generic fixtures were hard to keep in alignment and always seemed to break down at the worst time, right in the middle of a crunch run. As our devices became more sophisticated, other parameters that are difficult to control in a wire wrap fixture began to affect the measurements themselves. Inconsistencies such as improper lead lengths, parasitic inductance and loosening connections forced us to repeat the tests or, at worst, gave us false results that were not caught until much later in the process. Those old fixtures were costing us time and money."



A new semiconductor device is characterized by inserting it into a test fixture that provides support circuitry (for power, loads, I/O and other functions) and adapts it to instrumentation for the measurement of its key parameters. To ensure accurate measurements, the fixture must provide a stable, realistic environment for the device and it needs to withstand repeated insertions and removals without degrading its performance.

Galica continued, "Our fixtures were not keeping up with the demands of the new device technologies, but we could not let the designs out of our control for P.C. board fabrication. Designs are proprietary and extremely sensitive. Moreover, we do not have the time to wait for an outside vendor to respond. So, we just kept rebuilding and redesigning the fixtures to try to minimize the problems."

The Solution: Custom circuit card fixtures on the spot

One day, Scott Lynch, a Supertex Applications Engineer, showed Galica a prototype circuit board that had just been used to win a design contract. The board had been produced on their new circuit board plotter and had performed very well in the evaluation.



Galica recalled, "When I saw the quality of Scott’s demo board, I asked him to make us a test fixture board on the same plotter system. The results were excellent – solid performance and mechanical integrity – just what we needed, and it only took a couple of hours!".

The plotter system downloads files directly from a CAE program and translates them into board layouts. It then automatically produces each board by drilling the through holes and milling the traces from a variety of standard copper-clad FR3, FR4 and G10 laminated materials. Boards are cut to precise sizes and tolerances and most can be produced in a few minutes.



They tried using the plotter to redesign several other fixtures that had been particularly troublesome and found similar results. The plotter gave them close control over trace widths and spacing, proper routing of signal paths and optimum placement of parts. Connectors and sockets were precisely aligned and firmly attached for long, reliable lifetimes.

Best of all, the entire process resides in-house with complete security and instantaneous turnaround. The plotter system is kept in the design lab. No chemicals are used in this process and a built in vacuuming system keeps the area dust free.

The Bottom Line: Improved performance on the test floor, it is time for a second system

Frank Galica had several of his technicians trained in both CAE design and the board layout programs and they started 'borrowing' Scott’s plotter system on a regular basis. He reports, "We have made thousands of boards in the past few years. Our test times are significantly shorter and downtime for broken fixtures is non-existent. We are even making custom test equipment and custom panels for our test stations.

"Our only problem is that we need to get another system for Scott - the demand from the Test Department has taken over the machine and he is getting a little grumpy (smile)."

About Supertex

Supertex, Inc. is an IS0-9001-certified, publicly-held semiconductor manufacturer, focused on DMOS, HVCMOS and BiCMOS technology products for use in the computer, telecommunications, medical, instrumentation, defense and consumer product industries. The company designs and manufactures proprietary and industry-standard integrated circuits (ICs), and has earned international recognition as a demonstrated technological leader in high voltage and mixed signal high voltage semiconductor products. Headquarters is located in Sunnyvale, California.

About LPKF

LPKF Laser & Electronics is a wholly owned subsidiary of LPKF Laser & Electronics AG of Garbsen, Germany, a publicly traded company. Founded in 1976, LPKF has established itself on the international market in the fields of advanced circuit board prototyping, SMD stencils and high-density circuit board designs, eliminating the need for hazardous chemicals.  Their revolutionary MicroLine laser circuit structuring processes are transforming the design of smaller, lower cost, higher-performance products for tele-communications, computing, medical, video and measurement applications.

LPKF high precision circuit board plotters, multilayer devices and plating systems have become the standard of the industry with more than 8,000 installations worldwide. The drilling and milling process is simple, safe and economical. High precision tools and superior mechanical design turn circuit designs into holes and traces on a card by removing material. The ProtoMat® C30 plotter features repetition accuracy of 0.2 mils and it can produce traces as fine as 4 mils with spacing down to 8 mils. A typical card can be produced within 1-2 hours for $7 to $10 in materials and tools.