Good Old Man,
I wouldn't dare say to my friend that his job is 'overkill'! His boss asks him: we have boards from mobile telephones to radar applications and space, with lots of ceramic creeps that do not match mechanically very good. How will our products look after 5, 10, 20 and 30 years respectively in the field? What are your predictions? How many failures will we get and of what kind etc? What can we do to make our products even better? What parameters have then to be improved? What board material is best? What solder will prolong the products life even more? Etc. It's a multibillion-worth affair. By means of FEA etc, our friend has revealed many strange things that have been good for the company's health. So, from my aspect and despite your good reputation W., it can be worth some money to DfR. On the other hand, I did not mean to frighten the questioner; of course there are thumb rules that work good. Much depends on what he is really asking. As I also mentioned, we are bold enoug!
!
h to go against our own specialists sometimes, e.g. mounting 20mm large ceramic components on brass-board, really crazy. Our FEA man said it will never work, but it did, because we control the product's environment instead.
I just had to say against you W. Just a little..
Ingemar
Hi Ingemar,
I certainly would agree that 'Design for Reliability (DfR)' is necessary, in
this case and all others, to assure adequate long-term reliability of the
solder joints. However, for chip caps "FEA and solder joint CAD simulation
tools" are unnecessary overkill. For such a simple arrangement closed-form
equations will do nicely, see IPC-D-279. The more complex the modeling, the
more assumptions, often not very well founded ones, have to be made. FEA and
CAD tools are necessary for complex structures, such as BGAs, but not for CCs.
Werner Engelmaier
Engelmaier Associates, L.C.
Electronic Packaging, Interconnection and Reliability Consulting
7 Jasmine Run
Ormond Beach, FL 32174 USA
Phone: 904-437-8747, Fax: 904-437-8737
E-mail: [log in to unmask], Website: www.engelmaier.com
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