Wow! The Burn-in and Test Strategy (BiTS) Workshop just turned 15! The world of semiconductors has certainly changed over the years. And the BiTS Workshop has kept up with what is “Now & Next” in the burn-in and test of packaged integrated circuits (ICs). These achievements were celebrated in style by the more than three hundred participants at the recently held 2014 BiTS Workshop in Mesa, Arizona.
As the Burn-in & Test Strategies (BiTS) Workshop 2013 fades into the sunset (queue the music), here is a round-up of the highlights. There were gun fights in the corral as well as technical questions for the presenters. The saloon girls and gunfighters took an edge off of the “geek” factor. This year over three hundred fifty people come to the “Circle BiTS Ranch” (aka the Hilton in Mesa, Arizona) for the premier conference focused on what is new and next for semiconductor test tooling and strategy. Oh, did I mention that the theme this year was Western?
The “Post Personal Computer” (Post PC) era became the hot topic when Tim Cook introduced the latest iPad last week. Yes, calling it a “revolution” is definitely hype that is part of Apple‘s Post PC marketing campaign. Hype aside, it is clear that there has been a marked shift in digital hardware for the consumption of content and communication. The PC – be it a Windows, Mac, or Linux based system – is no longer “the device”. It is now one of many devices including portable music players (dominated by iPods), smart phones (lead by iPhones and Android based systems), and tablets (dominated by iPads). The shift is large and the impact is huge. To understand how big, watch the first three minutes of Mr. Cook’s presentation. Then you will understand why Apple had the largest market capitalization of any US company in February – the numbers are staggering.
Gert Hohenwarter, GateWave Northern, Inc., “Hidden Performance Limiters in the Signal Path”:
For high frequency signals, designers typically pay attention to avoiding coupling to adjacent signal lines to prevent cross talk. However, they need to look at many other areas of the design including coupling to power or sense lines, signal impedance mismatch, resonances, and the power distribution/delivery system (PDS). Coupling and mismatch may lead to resonances which reduce the operating speed or reduce the switching margin. These areas may also increase crosstalk increasing noise levels and also reducing switching margin. In addition, problems in the PDS may also reduce operating speed or switching margin. Continue reading “IEEE Semiconductor Wafer Test Workshop – Signal Integrity – Session Five (Tuesday)”
Mark McLaren, Integrated Technology Corporation, “Metrology Solutions for Very Large Probe Cards”:
Over the past few years as the number of memory devices to be tested in parallel has increased so has the size of probe cards to support this multisite testing. A few years ago memory probe cards grew to 440 mm diameter and recently they increased to 480 mm diameter. Now a similar growth in size has been seen for non-memory applications. Even though the parallelism (number of devices to be tested at once) has increased (but not on the scale of memory parallelism), the size increases have been the result of pushing more testing from package test to wafer test. These additional tests have required more local test resources (circuitry close to the device being tested) which require more real estate on probe cards. Continue reading “IEEE Semiconductor Wafer Test Workshop – Standards and Methods – Session Four (Monday)”
Balancing test coverage versus test cost. What does a test failure mean? Value of yield increase
… and how it impacts your bottom line!
A poorly implemented semiconductor test cell may pass integrated circuit (IC) parts that are either defective or have marginal performance. They can cause the electronic devices in which they will be assembled to either malfunction or completely fail. However, two other conditions require evaluation. Having false negative test “escapes” is expensive in terms of final product test failures, warranty costs, customer dissatisfaction, etc. In turn, the false positive test escapes needs to be balanced against the cost of false negative failures where otherwise good parts fail the tests and are discarded. Test engineers, product managers, quality engineers, and operational managers needs to make either implicit or explicit decisions as to the proper balance in adjusting the test limits. The goal is to cost effectively approach “zero defects” without “throwing out the baby with the bath water”.
A test process generally categorizes the item or device being tested as “pass” or “fail”. Sometimes passing devices are graded (typically by speed or other desired quality) and failing devices are often grouped by failure mode. “Coverage” is how well a particular test process measures the functionality and specifications of a given device. If every feature and specification is tested then it is said to have 100% test coverage. However, exhaustive testing is usually expensive due to long test times which translates in to operational costs including the depreciation of the test system and greater test setup complexity (equipment and development cost). Sometimes complete coverage is not possible or practical so there needs to be a trade-off between coverage and cost.