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need help in troubleshooting problem in my layout design with lan8742a
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me.rishabh12:
im facing a very strange issues on my design i soldered LAN8742a Ic which is in QFN24 package which have aground heat pad at the bottom
i soldered the ic using the hot air gun and not the problem is that it work normally for 2 to 3 hour sometime less or more
but after that it simply stop working and when once i reapply heat and solder it start working again but after that there is same issue
i just re soldered ic 3 to 4 times
can anyone explain whats going on my pcb and what is the exact issue
JS:
Reflowing the IC too many times could be a problem, their are rated for just a few cycles, 1 to 3 usually, IIRC.

Try changing the IC and using a lower temp solder, so you reduce the risk of potential damage to the new IC by overheating it.

JS

ajb:
How sure are you that the problem is with soldering, and that resoldering the chip is what's 'fixing' it? 

Does leaving the board powered off for a while make it work again?  Does hitting it with some cold spray make it work again? Does lightly heating the board make it fail more rapidly?

Are you absolutely sure that this behavior isn't the result of a software/network issue? 
me.rishabh12:
no turning off for long not fixing the problem and nor colling either
i need to use hot air gun to reflow solder then it will start working again

mrpackethead:
Post the schematics and board layouts.  I've used these by the bucketfull without issue, but layout is critical for reliable operation.
When its running what Voltage is at pin 6, ( VDDCR ).. Its very picky about having its gnd plane properly attached.     
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