Electromigration and/or dielectric erosion in FR4 substrates

Your data points were probably wet. Literally speaking that is.

Regards,

Boris Mohar

Got Knock? - see: Viatrack Printed Circuit Designs (among other things)

I wouldn't think that you would experience dielectric breakdown across

--Mac

Matt Roberds

Why not use Kapton as a substrate instead ?

Can you actually *get* 0.1 mm thick FR4 ?

Graham

on 4

Close, but it is 10 years with 100% utilization (all day every day), not 70 years:).

Syntactically, it's close: "twenty-four seven, three hundred sixty-five (and a quarter) days a year" sounds almost natural, since "twenty-four seven" means "continuously" in the vernacular.

Oops! Is the vokda kikcing in alradey?

If 7-11 stores are open 24 hours a day, howcome the doors have locks?

Cheers! Rich

Because, the stores were supposed to open at 7AM and close at 11PM.

look harder. 24*7*365*10 = 70 years. there are *NOT* 7*365.25 days in a year. To put it in perspective, the "normal" working year is 2,050 hours.

Cheers Terry

I have come across anecdotal evidence of low-voltage breakdown of FR4 as well. But I looked into the product in question (a commercial UPS), and found some pretty shonky layout/design/workmanship.

Firstly, the PCBs were all made somewhere in China, for the lowest price obtainable (100,000 per annum) no doubt using the cheapest, nastiest material known to man. Looking at half a dozen units, I saw significant variation in the LPI solder mask coverage and screen-printed overlay registration. I would suspect the process is neither clean nor consistent.

The design itself had acute angles, potentially allowing etchant to accumulate. bad CAD man. The copper width/thickness was also inadequate, and the high-current low voltage traces were discoloured. Standard 125C Tg (glass transition temperature) FR4 was used.

For our MIL products we stuck with a large, reputable PCB manufacturer with stringent process & quality control. We used high Tg FR4 (150C IIRC), and designed tracks for a 10C temperature rise (and considered dynamic thermal resistance too). And we very carefully cleaned then conformal coated our PCBs.

One faulty PCB was found thru hi-pot testing (17,000 commercial units) but that had a clearly visible lump of contaminant within the PCB material itself. Which came from China, but was cheap :)

Cheers Terry

Okay,

I am sufficiently embarrassed.