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How can I troubleshoot an active short circuit?
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What are some effective methods of diagnosing an active short circuit? By this I mean a short circuit that presents itself only after a PCB is powered on.
tl;dr
I have a design in the prototype phase. 17 of my 20 boards work great. The other 3 all have a short circuit on a 3.3V rail. This only shows up after the board is powered on. After removing most of the components on the rail, I tracked it down to an Ethernet PHY. If I lift the IC off, my rail is rock-solid at 3.3V. When I put it back on (also tried 2 new ICs), my rail is overloaded again and it drops out.
I have thoroughly visually inspected, and probed the board for shorts, but cannot find one. I have lifted off pretty much everything around the IC (crystal, series resistors, ferrite beads, etc.) but still get the same behaviour. I've also tried holding the chip in reset, but that doesn't help.
I lifted individual pins on the IC (VDDIO) and that fixed it, but doesn't offer a real diagnosis. I'm starting to wonder if there's an issue with the PCB fab, but not totally sure how it would cause this. They claim to do 100% E-test. Any advice will be appreciated!
short-circuit
asked 1 hour ago
Kane Anderson
1907
 |Â
show 1 more comment
up vote
2
down vote
favorite
What are some effective methods of diagnosing an active short circuit? By this I mean a short circuit that presents itself only after a PCB is powered on.
tl;dr
I have a design in the prototype phase. 17 of my 20 boards work great. The other 3 all have a short circuit on a 3.3V rail. This only shows up after the board is powered on. After removing most of the components on the rail, I tracked it down to an Ethernet PHY. If I lift the IC off, my rail is rock-solid at 3.3V. When I put it back on (also tried 2 new ICs), my rail is overloaded again and it drops out.
I have thoroughly visually inspected, and probed the board for shorts, but cannot find one. I have lifted off pretty much everything around the IC (crystal, series resistors, ferrite beads, etc.) but still get the same behaviour. I've also tried holding the chip in reset, but that doesn't help.
I lifted individual pins on the IC (VDDIO) and that fixed it, but doesn't offer a real diagnosis. I'm starting to wonder if there's an issue with the PCB fab, but not totally sure how it would cause this. They claim to do 100% E-test. Any advice will be appreciated!
short-circuit
asked 1 hour ago
Kane Anderson
1907
Do have access to a scope to pulse 1A thru the short for 1us? WHat is the DRC gap tolerance and actual? Was there any chance of ESD damage and shoot thru fault?
– Tony EE rocketscientist
1 hour ago
Yes, I have a decent scope. I can try pulsing power through it and see what I can learn. What exactly am I looking for?
– Kane Anderson
59 mins ago
Is it a multilayer pcb with internal layers? Does the layout include any fiducial marks to verify correct layer-to-layer registration? Do you have an infrared / thermal inspection camera? ... If you've got all the ICs off and the short persists, can you put a really high current through the short and see where the smoke comes out?
– MarkU
58 mins ago
Our techs since the early 80's always used a micro-ohm meter to apply a small voltage and follow the voltage drops. If there was a buried short on a via to gnd plane say >50m Ohms it could be fused open by a Cap dump discharge. with a Cap with similar or much lower ESR and sufficient welding energy but not too much to spray the void with metallic dust in the junction. Excess solder heat can often close small via gaps. Beware of port case ground touching exposed vias. 100% E test is a paid service. So make sure it was not your process fault.
– Tony EE rocketscientist
58 mins ago
If possible, connect a supply to 3.3V that is capable of delivering lots of current. Then watch with a thermal imaging camera. The short circuit area should heat up quickly. This test may end up being destructive. The more power you deliver to the short, the more resolution you will have to locate it. So try to get a supply that can hold 3.3V into whatever the short circuit current is.
– mkeith
36 mins ago
 |Â
show 1 more comment
up vote
2
down vote
favorite
up vote
2
down vote
favorite
What are some effective methods of diagnosing an active short circuit? By this I mean a short circuit that presents itself only after a PCB is powered on.
tl;dr
I have a design in the prototype phase. 17 of my 20 boards work great. The other 3 all have a short circuit on a 3.3V rail. This only shows up after the board is powered on. After removing most of the components on the rail, I tracked it down to an Ethernet PHY. If I lift the IC off, my rail is rock-solid at 3.3V. When I put it back on (also tried 2 new ICs), my rail is overloaded again and it drops out.
I have thoroughly visually inspected, and probed the board for shorts, but cannot find one. I have lifted off pretty much everything around the IC (crystal, series resistors, ferrite beads, etc.) but still get the same behaviour. I've also tried holding the chip in reset, but that doesn't help.
I lifted individual pins on the IC (VDDIO) and that fixed it, but doesn't offer a real diagnosis. I'm starting to wonder if there's an issue with the PCB fab, but not totally sure how it would cause this. They claim to do 100% E-test. Any advice will be appreciated!
short-circuit
asked 1 hour ago
Kane Anderson
1907
What are some effective methods of diagnosing an active short circuit? By this I mean a short circuit that presents itself only after a PCB is powered on.
tl;dr
I have a design in the prototype phase. 17 of my 20 boards work great. The other 3 all have a short circuit on a 3.3V rail. This only shows up after the board is powered on. After removing most of the components on the rail, I tracked it down to an Ethernet PHY. If I lift the IC off, my rail is rock-solid at 3.3V. When I put it back on (also tried 2 new ICs), my rail is overloaded again and it drops out.
I have thoroughly visually inspected, and probed the board for shorts, but cannot find one. I have lifted off pretty much everything around the IC (crystal, series resistors, ferrite beads, etc.) but still get the same behaviour. I've also tried holding the chip in reset, but that doesn't help.
I lifted individual pins on the IC (VDDIO) and that fixed it, but doesn't offer a real diagnosis. I'm starting to wonder if there's an issue with the PCB fab, but not totally sure how it would cause this. They claim to do 100% E-test. Any advice will be appreciated!
short-circuit
short-circuit
asked 1 hour ago
Kane Anderson
1907
asked 1 hour ago
Kane Anderson
1907
asked 1 hour ago
Kane Anderson
1907
asked 1 hour ago
Kane Anderson
1907
asked 1 hour ago
Kane Anderson
1907
1907
Do have access to a scope to pulse 1A thru the short for 1us? WHat is the DRC gap tolerance and actual? Was there any chance of ESD damage and shoot thru fault?
– Tony EE rocketscientist
1 hour ago
Yes, I have a decent scope. I can try pulsing power through it and see what I can learn. What exactly am I looking for?
– Kane Anderson
59 mins ago
Is it a multilayer pcb with internal layers? Does the layout include any fiducial marks to verify correct layer-to-layer registration? Do you have an infrared / thermal inspection camera? ... If you've got all the ICs off and the short persists, can you put a really high current through the short and see where the smoke comes out?
– MarkU
58 mins ago
Our techs since the early 80's always used a micro-ohm meter to apply a small voltage and follow the voltage drops. If there was a buried short on a via to gnd plane say >50m Ohms it could be fused open by a Cap dump discharge. with a Cap with similar or much lower ESR and sufficient welding energy but not too much to spray the void with metallic dust in the junction. Excess solder heat can often close small via gaps. Beware of port case ground touching exposed vias. 100% E test is a paid service. So make sure it was not your process fault.
– Tony EE rocketscientist
58 mins ago
If possible, connect a supply to 3.3V that is capable of delivering lots of current. Then watch with a thermal imaging camera. The short circuit area should heat up quickly. This test may end up being destructive. The more power you deliver to the short, the more resolution you will have to locate it. So try to get a supply that can hold 3.3V into whatever the short circuit current is.
– mkeith
36 mins ago
 |Â
show 1 more comment
Do have access to a scope to pulse 1A thru the short for 1us? WHat is the DRC gap tolerance and actual? Was there any chance of ESD damage and shoot thru fault?
– Tony EE rocketscientist
1 hour ago
Yes, I have a decent scope. I can try pulsing power through it and see what I can learn. What exactly am I looking for?
– Kane Anderson
59 mins ago
Is it a multilayer pcb with internal layers? Does the layout include any fiducial marks to verify correct layer-to-layer registration? Do you have an infrared / thermal inspection camera? ... If you've got all the ICs off and the short persists, can you put a really high current through the short and see where the smoke comes out?
– MarkU
58 mins ago
Our techs since the early 80's always used a micro-ohm meter to apply a small voltage and follow the voltage drops. If there was a buried short on a via to gnd plane say >50m Ohms it could be fused open by a Cap dump discharge. with a Cap with similar or much lower ESR and sufficient welding energy but not too much to spray the void with metallic dust in the junction. Excess solder heat can often close small via gaps. Beware of port case ground touching exposed vias. 100% E test is a paid service. So make sure it was not your process fault.
– Tony EE rocketscientist
58 mins ago
If possible, connect a supply to 3.3V that is capable of delivering lots of current. Then watch with a thermal imaging camera. The short circuit area should heat up quickly. This test may end up being destructive. The more power you deliver to the short, the more resolution you will have to locate it. So try to get a supply that can hold 3.3V into whatever the short circuit current is.
– mkeith
36 mins ago
Do have access to a scope to pulse 1A thru the short for 1us? WHat is the DRC gap tolerance and actual? Was there any chance of ESD damage and shoot thru fault?
– Tony EE rocketscientist
1 hour ago
Do have access to a scope to pulse 1A thru the short for 1us? WHat is the DRC gap tolerance and actual? Was there any chance of ESD damage and shoot thru fault?
– Tony EE rocketscientist
1 hour ago
Yes, I have a decent scope. I can try pulsing power through it and see what I can learn. What exactly am I looking for?
– Kane Anderson
59 mins ago
Yes, I have a decent scope. I can try pulsing power through it and see what I can learn. What exactly am I looking for?
– Kane Anderson
59 mins ago
Is it a multilayer pcb with internal layers? Does the layout include any fiducial marks to verify correct layer-to-layer registration? Do you have an infrared / thermal inspection camera? ... If you've got all the ICs off and the short persists, can you put a really high current through the short and see where the smoke comes out?
– MarkU
58 mins ago
Is it a multilayer pcb with internal layers? Does the layout include any fiducial marks to verify correct layer-to-layer registration? Do you have an infrared / thermal inspection camera? ... If you've got all the ICs off and the short persists, can you put a really high current through the short and see where the smoke comes out?
– MarkU
58 mins ago
Our techs since the early 80's always used a micro-ohm meter to apply a small voltage and follow the voltage drops. If there was a buried short on a via to gnd plane say >50m Ohms it could be fused open by a Cap dump discharge. with a Cap with similar or much lower ESR and sufficient welding energy but not too much to spray the void with metallic dust in the junction. Excess solder heat can often close small via gaps. Beware of port case ground touching exposed vias. 100% E test is a paid service. So make sure it was not your process fault.
– Tony EE rocketscientist
58 mins ago
Our techs since the early 80's always used a micro-ohm meter to apply a small voltage and follow the voltage drops. If there was a buried short on a via to gnd plane say >50m Ohms it could be fused open by a Cap dump discharge. with a Cap with similar or much lower ESR and sufficient welding energy but not too much to spray the void with metallic dust in the junction. Excess solder heat can often close small via gaps. Beware of port case ground touching exposed vias. 100% E test is a paid service. So make sure it was not your process fault.
– Tony EE rocketscientist
58 mins ago
If possible, connect a supply to 3.3V that is capable of delivering lots of current. Then watch with a thermal imaging camera. The short circuit area should heat up quickly. This test may end up being destructive. The more power you deliver to the short, the more resolution you will have to locate it. So try to get a supply that can hold 3.3V into whatever the short circuit current is.
– mkeith
36 mins ago
If possible, connect a supply to 3.3V that is capable of delivering lots of current. Then watch with a thermal imaging camera. The short circuit area should heat up quickly. This test may end up being destructive. The more power you deliver to the short, the more resolution you will have to locate it. So try to get a supply that can hold 3.3V into whatever the short circuit current is.
– mkeith
36 mins ago
 |Â
show 1 more comment
2 Answers
2
active
oldest
votes
up vote
5
down vote
It won't always work, but sometimes you can track down a short with a thermal camera... of course you have to have a thermal camera to do that.
Just power the bored up and watch very closely through the thermal camera to see if one area of the board gets really hot, could help you narrow down the area at least.
answered 1 hour ago
nonya_business
511
New contributor
nonya_business is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
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1
Thanks, I will give that a try. I do have access to one.
– Kane Anderson
58 mins ago
Yeah I was about to suggest a thermal camera. My reliability and failure analysis team at work have these and it's super obvious when something is short circuited. It's pretty cool to look at as well :)
– KingDuken
49 mins ago
It is viable to use a bench PSU to dump a lot of current and find the hot spot with your hands as well.
– Wesley Lee
35 mins ago
add a comment |Â
up vote
0
down vote
can you try exchange PHY IC with a working board to see what happen? So if fault migrate between board we can pinpoint PCB can be defective/IC got damaged by.
What king of PHY are you using?
Are all Static precaution and handling in place at assembly?
Regards
Roberto
answered 53 mins ago
roberto romano
11
New contributor
roberto romano is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
add a comment |Â
2 Answers
2
active
oldest
votes
2 Answers
2
active
oldest
votes
active
oldest
votes
active
oldest
votes
up vote
5
down vote
It won't always work, but sometimes you can track down a short with a thermal camera... of course you have to have a thermal camera to do that.
Just power the bored up and watch very closely through the thermal camera to see if one area of the board gets really hot, could help you narrow down the area at least.
answered 1 hour ago
nonya_business
511
New contributor
nonya_business is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
1
Thanks, I will give that a try. I do have access to one.
– Kane Anderson
58 mins ago
Yeah I was about to suggest a thermal camera. My reliability and failure analysis team at work have these and it's super obvious when something is short circuited. It's pretty cool to look at as well :)
– KingDuken
49 mins ago
It is viable to use a bench PSU to dump a lot of current and find the hot spot with your hands as well.
– Wesley Lee
35 mins ago
add a comment |Â
up vote
5
down vote
It won't always work, but sometimes you can track down a short with a thermal camera... of course you have to have a thermal camera to do that.
Just power the bored up and watch very closely through the thermal camera to see if one area of the board gets really hot, could help you narrow down the area at least.
answered 1 hour ago
nonya_business
511
New contributor
nonya_business is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
1
Thanks, I will give that a try. I do have access to one.
– Kane Anderson
58 mins ago
Yeah I was about to suggest a thermal camera. My reliability and failure analysis team at work have these and it's super obvious when something is short circuited. It's pretty cool to look at as well :)
– KingDuken
49 mins ago
It is viable to use a bench PSU to dump a lot of current and find the hot spot with your hands as well.
– Wesley Lee
35 mins ago
add a comment |Â
up vote
5
down vote
up vote
5
down vote
It won't always work, but sometimes you can track down a short with a thermal camera... of course you have to have a thermal camera to do that.
Just power the bored up and watch very closely through the thermal camera to see if one area of the board gets really hot, could help you narrow down the area at least.
answered 1 hour ago
nonya_business
511
New contributor
nonya_business is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
It won't always work, but sometimes you can track down a short with a thermal camera... of course you have to have a thermal camera to do that.
Just power the bored up and watch very closely through the thermal camera to see if one area of the board gets really hot, could help you narrow down the area at least.
answered 1 hour ago
nonya_business
511
New contributor
nonya_business is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
answered 1 hour ago
nonya_business
511
New contributor
nonya_business is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
answered 1 hour ago
nonya_business
511
answered 1 hour ago
nonya_business
511
511
New contributor
nonya_business is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
New contributor
nonya_business is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
nonya_business is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
1
Thanks, I will give that a try. I do have access to one.
– Kane Anderson
58 mins ago
Yeah I was about to suggest a thermal camera. My reliability and failure analysis team at work have these and it's super obvious when something is short circuited. It's pretty cool to look at as well :)
– KingDuken
49 mins ago
It is viable to use a bench PSU to dump a lot of current and find the hot spot with your hands as well.
– Wesley Lee
35 mins ago
add a comment |Â
1
Thanks, I will give that a try. I do have access to one.
– Kane Anderson
58 mins ago
Yeah I was about to suggest a thermal camera. My reliability and failure analysis team at work have these and it's super obvious when something is short circuited. It's pretty cool to look at as well :)
– KingDuken
49 mins ago
It is viable to use a bench PSU to dump a lot of current and find the hot spot with your hands as well.
– Wesley Lee
35 mins ago
1
1
Thanks, I will give that a try. I do have access to one.
– Kane Anderson
58 mins ago
Thanks, I will give that a try. I do have access to one.
– Kane Anderson
58 mins ago
Yeah I was about to suggest a thermal camera. My reliability and failure analysis team at work have these and it's super obvious when something is short circuited. It's pretty cool to look at as well :)
– KingDuken
49 mins ago
Yeah I was about to suggest a thermal camera. My reliability and failure analysis team at work have these and it's super obvious when something is short circuited. It's pretty cool to look at as well :)
– KingDuken
49 mins ago
It is viable to use a bench PSU to dump a lot of current and find the hot spot with your hands as well.
– Wesley Lee
35 mins ago
It is viable to use a bench PSU to dump a lot of current and find the hot spot with your hands as well.
– Wesley Lee
35 mins ago
add a comment |Â
up vote
0
down vote
can you try exchange PHY IC with a working board to see what happen? So if fault migrate between board we can pinpoint PCB can be defective/IC got damaged by.
What king of PHY are you using?
Are all Static precaution and handling in place at assembly?
Regards
Roberto
answered 53 mins ago
roberto romano
11
New contributor
roberto romano is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
add a comment |Â
up vote
0
down vote
can you try exchange PHY IC with a working board to see what happen? So if fault migrate between board we can pinpoint PCB can be defective/IC got damaged by.
What king of PHY are you using?
Are all Static precaution and handling in place at assembly?
Regards
Roberto
answered 53 mins ago
roberto romano
11
New contributor
roberto romano is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
add a comment |Â
up vote
0
down vote
up vote
0
down vote
can you try exchange PHY IC with a working board to see what happen? So if fault migrate between board we can pinpoint PCB can be defective/IC got damaged by.
What king of PHY are you using?
Are all Static precaution and handling in place at assembly?
Regards
Roberto
answered 53 mins ago
roberto romano
11
New contributor
roberto romano is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
can you try exchange PHY IC with a working board to see what happen? So if fault migrate between board we can pinpoint PCB can be defective/IC got damaged by.
What king of PHY are you using?
Are all Static precaution and handling in place at assembly?
Regards
Roberto
answered 53 mins ago
roberto romano
11
New contributor
roberto romano is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
answered 53 mins ago
roberto romano
11
New contributor
roberto romano is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
answered 53 mins ago
roberto romano
11
answered 53 mins ago
roberto romano
11
11
New contributor
roberto romano is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
New contributor
roberto romano is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
roberto romano is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
add a comment |Â
add a comment |Â
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Do have access to a scope to pulse 1A thru the short for 1us? WHat is the DRC gap tolerance and actual? Was there any chance of ESD damage and shoot thru fault?
– Tony EE rocketscientist
1 hour ago
Yes, I have a decent scope. I can try pulsing power through it and see what I can learn. What exactly am I looking for?
– Kane Anderson
59 mins ago
Is it a multilayer pcb with internal layers? Does the layout include any fiducial marks to verify correct layer-to-layer registration? Do you have an infrared / thermal inspection camera? ... If you've got all the ICs off and the short persists, can you put a really high current through the short and see where the smoke comes out?
– MarkU
58 mins ago
Our techs since the early 80's always used a micro-ohm meter to apply a small voltage and follow the voltage drops. If there was a buried short on a via to gnd plane say >50m Ohms it could be fused open by a Cap dump discharge. with a Cap with similar or much lower ESR and sufficient welding energy but not too much to spray the void with metallic dust in the junction. Excess solder heat can often close small via gaps. Beware of port case ground touching exposed vias. 100% E test is a paid service. So make sure it was not your process fault.
– Tony EE rocketscientist
58 mins ago
If possible, connect a supply to 3.3V that is capable of delivering lots of current. Then watch with a thermal imaging camera. The short circuit area should heat up quickly. This test may end up being destructive. The more power you deliver to the short, the more resolution you will have to locate it. So try to get a supply that can hold 3.3V into whatever the short circuit current is.
– mkeith
36 mins ago