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Dead / open circuit SMT resistor
MUFF WIGGLER Forum Index -> Music Tech DIY  
Author Dead / open circuit SMT resistor
forestcaver
Just curious if anyone else has had a SMT resistor fail?
I built two MI Ripples. One worked fine but the other was a pain to debug. One of the 33k resistors in the filter cascade block was dead (open). I dont
believe that I heated it up any more than the others - just touched it briefly (~1s) with a 300 deg C temp-controlled iron (ERSA). It was a Yageo .1w, 75v resistor. The datasheet says (like panasonic) soldering temp exposure is 260 deg C for 10s. I used leaded solder.
Removing it and testing it showed that it was open. Replacing it everything worked fine.
I was really surprised it was dead - wonder if it was technique or faulty resistor.
This was my first go at SMT work and overall found it pretty ok.
With through hole I test all components first.

Questions
Anyone else had problems like this?
Is it more likely to be my technique or a faulty component? (I think I was fine - all the other components and ICs were fine)
Do you test components (0603) before placing?
Should I be using a lower temp to solder?
onre
Haven't ever had this happen, and I'm a rather careless SMT solderer. I'd bet on a faulty component.
forestcaver
Onre - thanks - that’s reassuring!
emmaker
I've never had problems with SMT resistors and I never test them. Well unless I get them mixed up and can't read the values printed on them. I've overheated some caps and destroyed them.

Another thing, did you use sharp metal tools to place and hold them?

I use metal tweezers to very carefully place parts but use a round wood toothpick with the tip cut off to hold them while soldering.

SMT resistors are pieces of ceramic with a resistive coating on them. If that coating gets scratched (from a sharp metal tool) it can affect the resistance and the circuit can have problems. You'll have either a higher resistance or an open part.

Another problem if to much solder is used a solder bridge under the part can occur which will result in a complete short or very low resistance.
forestcaver
emmaker wrote:

Another thing, did you use sharp metal tools to place and hold them?


I did use a pair of metal tweezers (no serrations, flat gripping surface) and
held all the resistors very gently as I was scared of them pinging off !

emmaker wrote:

SMT resistors are pieces of ceramic with a resistive coating on them. If that coating gets scratched (from a sharp metal tool) it can affect the resistance and the circuit can have problems. You'll have either a higher resistance or an open part.


Didnt know that - cheers. The resistor was open. I looked at it with high magnification and couldn't see marks or anything (I was looking for burn marks/discolouration, etc and not specifically scratches but I think I would have noticed anything obvious - but who knows :-) )

Thanks for the info. Will be careful handling them in future....

Cheers....
toneburst
I've done quite a few primarily surface-mount projects, now, and never had a blown resistor.

I'm with @emmaker- could have been a bridge underneath the component. I've never had this happen, either, but I suspect its a more likely explanation than a dodgy resistor.

a|x
forestcaver
toneburst wrote:
I've done quite a few primarily surface-mount projects, now, and never had a blown resistor.

I'm with @emmaker- could have been a bridge underneath the component. I've never had this happen, either, but I suspect its a more likely explanation than a dodgy resistor.

a|x


H Toneburst - not sure I understand - if there was a solder bridge the resistance acroo the resistor would be low to zero, surely (?????) This resistor measured very high in-circuit and open once desoldered....
toneburst
Ah, I must heave misread, sorry.
forestcaver
thumbs up
Ryzyn
If this is the case in any future builds, would the correct method of troubleshooting be to continuity test all the resistors on the board?
forestcaver
Ryzyn wrote:
If this is the case in any future builds, would the correct method of troubleshooting be to continuity test all the resistors on the board?


Or measure the resistance! Because of other possible paths an open resistor tested in-circuit could very was well signal continuity....
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