Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!mailrus!cs.utexas.edu!wuarchive!wugate!uunet!sjsca4!chomolungma!poffen From: poffen@chomolungma (Russ Poffenberger) Newsgroups: comp.sys.ibm.pc Subject: Re: engineering margins (or, living on the edge...) Message-ID: <1989Nov14.175344.8839@sj.ate.slb.com> Date: 14 Nov 89 17:53:44 GMT References: <1989Nov10.214341.4071@ico.isc.com> <1989Nov12.154710.25669@mccc.uucp> Reply-To: poffen@sj.ate.slb.com (Russ Poffenberger) Distribution: na Organization: Schlumberger ATE, San Jose, CA Lines: 65 In article <1989Nov12.154710.25669@mccc.uucp> pjh@mccc.UUCP (Pete Holsberg) writes: > >My experience in manufacturing electronic components (granted, it was a >long time ago) suggests that reliability is not guaranteed no matter >what. A manufacturer tests a part say for speed, and on the basis of >actual performance, places each device into a separate category. For >example, if a 386 performs OK during the 25 MHz test, it's marked >"25MHz", If not, it's tested for 20MHz, etc. To be sure, some kind of >life testing is usually done to ensure that the test itself is reliable. > But on the other hand, I'll bet that testing is done statistically, >i.e., a sample of a batch of devices is tested and on the basis of the >test results, the entire batch is categorized. > >Perhaps the safest approach is to derate the parts: use a 25MHz part at >20MHz, just to be sure that "drift" never gets you in trouble during the >lifetime of the device. > OK. You guys asked for it, here is what most companies do about testing parts. I think I am qualified because I have worked for 5 years with a company that makes testers to test these types of devices. Note that different manufacturers have different strategies, and these strategies may vary between different types of parts. (ie memory devices may be tested differently from uP's or ASIC's) Virtually all parts are tested and categorized for speed (if applicable). Sometimes manufacturers will run extended characterization tests on select parts (every hundred or so). The Speed categorization is much like mentioned above, the parts are tested at the most demanding speed, and if they fail, may be downgraded to a slower test and tried there. This process repeats with the standard speed categories until the part passes one of them, or fails all tests in which case it is trashed. Note that the testing often is more complicated than just speed categories. They may also be tested at various speed and voltage settings. They may also be tested ate the wafer level (before packaging) to determine parts that may possibly meet Mil requirements. Occasionally, parts may be never be tested at the maximum speed possible due to market conditions. If the latest demand is for 20Mhz parts, they may skip the 25Mhz tests altogether in order to fill market demand. In this case, you may get a part that can run at a faster speed, but you have no way of knowing. Even when parts pass a certain speed category, it is usually done at more rigorous conditions than you usually see in its final application. Usually they are elevated and chilled in temperature, and run at both high and low VCC. My judgement is that a part should only be run at its rated speed. Running it faster may work and never give problems, but running it faster may do other things like make it run hotter than normal, and the cooling of the computer may not handle it well enough (note that all parts in the computer, not just the CPU run faster and generate more heat) and the parts may fail at these elevated temperatures. Russ Poffenberger DOMAIN: poffen@sj.ate.slb.com Schlumberger Technologies UUCP: {uunet,decwrl,amdahl}!sjsca4!poffen 1601 Technology Drive CIS: 72401,276 San Jose, Ca. 95110 (408)437-5254 ------------------------- In a dictatorship, people suffer without complaining. In a democracy, people complain without suffering.