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I am looking to understand physical pressure induced characteristic changes in reagrds to the the following two Op Amps:
LMV551MG/NOPB and OPA314AIDCKR (SC70 Pacakges).
The circuit containing the Op Amp (one or the other) is potted/overmolded which results in potential pressures of several hundred psi and temperatures up to 100C. How does the mechanical stress affect both of these devices and is one better designed to handle the added stress? We have seen small voltage changes in the LMV551 after the molding process.
FYI... This issue was not originally present in our product (with the LMV551) until Jan 2012. Has there been any changes to the LMV551 over the last year?
Exerting physical pressure on any op amp will cause banding/twisting forces on the die inside the package - in most cases, this will result most noticeably in a shift in the input voltage offset and drift. The mechanical stress exerted by the molding process and the resulting parametric shifts are already reflected in the PDS spec table.
Any external mechanical stress conditions are for obvious reasons NOT applied during the final test and thus may result in Vos and drift NOT meeting PDS limits. Since we do not test any of our products under such conditions, we may NOT attest to the differences in any potential shifts between LMV551 and OPA314. However, as a general rule, a larger package should provide greater immunity to mechanically-induced shifts due to better ability to resist banding/twisting forces.
Marek Lis, MGTSSr Application EngineerPrecision Analog - TI Tucson
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I'll second Marek's comments....we cannot test for every combination of stresses, physical and electrical, customers seem to come up with...
The SC-70 package leaves very little "meat" to dissipate stresses - so a lot of the stress does make it to the die. The leads can be sensitive to pressure as they can exert quite a bit of leverage on the package material when flexed. It is very easy to crack the SC-70 package in half by twisting the leads (because there is so little "meat" between the leads). The LMV551 is not a particularly "precision" device - so the die may be a bit more sensitive to stresses.
What are the datecodes and/or markings on the device? This would help us pin down when the device was manufactured and what lot it came from. This info should also be on the box/reel the devices came packaged in.
Looking at the history, the LMV551 transferred fabs, and also had a plating change, in late 2010. It's not uncommon for the finished product to sit on various shelves for a year before being delivered to the customer - so it could be from this time frame.
TI Comparators (CMPS) Applications Group
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