In an effort to reduce the cost-of-test (COT), a number of customers are increasing the parallelism of logic wafer probe cards. However, due to the complexity such as pitch and number of probes, the pricing for these cards is reaching astronomical levels. We do not believe this trend is sustainable, let alone logical. The presentation suggested examples of alternative solutions. It is clear that critical solutions need to be optimized at the test cell, factory, and supply chain level not just at the consumable (probe card) level.
Integrated circuits using 2.5D advanced packaging are shipping. 3D packaging with thru-silicon vias (TSV) has been demonstrated. “5.5D” packages may not be far behind. Probe card suppliers have made progress building interconnect technology for the micro-bump arrays. Standards committees have started defining IC interface standards and test access protocols.
But what does the Test Engineer and Management really want? What can they afford? What are the most likely scenarios? Factors that determine which test technology can support the desired test flow are examined. In particular, probe card technology for probing TSV bumps and potential usage models are reviewed.
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?
Larry Levy (FormFactor, Inc.), “Is Parametric Testing About To Enter a Period of Growth and Innovation?”:
Upwards of one thousand facilities perform parametric wafer testing (based on 2009 market data) with over a third of these using obsolete test equipment. There have been no really new testers in several years – Agilent still has their 40xx series and Keithley has their S530 tester. And several companies have exited the market and some companies (including Keithley) are no longer supporting older models of testers. Since parametric testing remains an essential process, this has forced a high number of these facilities to use obsolete equipment or find other approaches. A few companies are going as far as using an Advantest 93000, a significantly more expensive and highly sophisticated digital tester, for parametric test. [Updated to clarify Keithley’s status.]
This year’s IEEESemiconductor Wafer Test Workshop started on Sunday June 10th with a pleasant surprise. Due to a welcomed but unexpected wave of seventy walk-in registrations, there was insufficient seating at the opening dinner. Thankfully the hotel staff quickly adjusted to accommodate these additional guests. Attendance and interest in this year’s workshop was clearly up.
Jerry Broz, general conference chair, welcomed everyone with a brief overview and presented prizes for the first annual golf tournament. We then quickly proceeded with business as Matt Nowak (Senior Director, Advanced Technology, Qualcomm CDMA Technologies) provided the keynote “Emerging High Density 3D Through Silicon Stacking (TSS) – What’s Next?” Mr. Nowak discussed the increased amount of hype within the 3D semiconductor packaging market in the last year with everyone announcing something. And Thru Silicon Vias (TSVs) technology has already been in high volume production for image sensors for several years now but at a significantly lower density than for 3D packaging.
As the final presenter at this week’s IEEESemiconductor Wafer Test Workshop (SWTW), I outlined how critical it is to understand the true cost of a product’s architecture in “Probe Card Cost Drivers from Architecture to Zero Defects“. Without a proper understanding of these costs – especially for fully custom high technology products such as wafer test probe cards – it is impossible to maintain a sufficient gross margin. Gross margin is essential to maintain the health of a company and to fund the research & development required for innovation.
Yes, there were a few in the audience who appeared pleased since they are confident that their products are on the right path. There were others who may have been upset based upon their company’s direction. I would argue that a proper diagnosis – regardless of how disturbing – is essential to drive the proper cure.
There is plenty of opportunity in the test market and reasons for optimism. The key to long term prosperity is to really understand the fundamentals of the business and not be blinded by the technology.
I thank those who stayed for the entire conference and welcome your thoughts below. And I will be posting more about the conference (including my summaries) in the next few weeks.
Even though this sounds like the start of a Carnac the Magnificent comedy act, these are some of the answers from my Probe Card Market model. I keep my model current so I know both industry and company specific performance as well as to make predictions. You don’t have a model? Are you reacting instead of predicting?
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.