iPhone 6s PMIC keeps shorting - GSM-Forum

short_toground · 01-16-2017, 04:47

Replaced PMIC twice and still it gets hot when connected to power with no boot, instant short circuit with bench power supply.

Remove PMIC, short gone. Only there when installed.

Any ideas?

zarbourne · 01-16-2017, 04:54

Are you sure there is no short after you remove PMIC? Are you testing for short with DCPS or multimeter?

You need to look on ZXW or Pads and see all the different lines/netnames that connect to PMIC and test for short with multimeter!

short_toground · 01-16-2017, 04:56

Quote:

Originally Posted by zarbourne

Are you sure there is no short after you remove PMIC? Are you testing for short with DCPS or multimeter?

You need to look on ZXW or Pads and see all the different lines/netnames that connect to PMIC and test for short with multimeter!

I'm sure I'm testing with a multimeter in diode mode and beep mode.

When PMIC in place there's a short on vcc_main and only pmic gets hot.

Remove pmic and no short on vcc_main

zarbourne · 01-16-2017, 05:04

ok thats good, when you clean solder of pads under pmic make sure that there isn't exposed lines, thats why I never use solderwick to clean solder I remove solder with the soldering iron and flux and leave small solder on pads, not flat!

After that I put a little flux on pads so they help stick, then I align PMIC and push down (NOT TOO HARD!) and it is stuck. Then I look under microscope with board on angle so i can see if PMIC is aligned properly, then apple heat. That is perfect way in my opinion.

short_toground · 01-16-2017, 05:09

Quote:

Originally Posted by zarbourne

ok thats good, when you clean solder of pads under pmic make sure that there isn't exposed lines, thats why I never use solderwick to clean solder I remove solder with the soldering iron and flux and leave small solder on pads, not flat!

After that I put a little flux on pads so they help stick, then I align PMIC and push down (NOT TOO HARD!) and it is stuck. Then I look under microscope with board on angle so i can see if PMIC is aligned properly, then apple heat. That is perfect way in my opinion.

Thanks. I never use solderwick to clean pads. You think it could be a solder issue?

zarbourne · 01-16-2017, 05:15

Maybe, like in this picture you can see a track is a little exposed so sometimes solder can connect 2 pads after you put PMIC on. Hard for me to know where the short is without the phone infront of me.

short_toground · 01-16-2017, 05:17

Oh ok I'll double check the pads

zarbourne · 01-16-2017, 05:17

Also, if you're reballing the pmic, and still short, then there is chance pmic is faulty, in which case put new one or one from other board

short_toground · 01-16-2017, 18:52

What's the best tip to use for cleaning pads?

I've been using this one

Kradziej · 01-16-2017, 20:55

2nd visible from left
but that looks like cheap chinese soldering iron so you are probably going to lift some pads with it be careful, dont slide over just press to the board

short_toground · 01-16-2017, 21:08

So I'm testing the vcc_main points on the PCB with pmic removed and I measure multiple shorts to ground but if I measure vcc_main from another spot like a capacitor it doesn't read shorted. Only at the pmic pins

Kradziej · 01-16-2017, 21:11

then you have incorrect schematics or you measure in incorrect places by mistake, there is no other way

short_toground · 01-17-2017, 01:20

Quote:

Originally Posted by Kradziej

2nd visible from left
but that looks like cheap chinese soldering iron so you are probably going to lift some pads with it be careful, dont slide over just press to the board

Why 2nd from left? Does it pick up solder from pads better than the rest?

Kradziej · 01-17-2017, 04:23

Quote:

Originally Posted by short_toground

Why 2nd from left? Does it pick up solder from pads better than the rest?

big, flat surface gives you proper and even heat transfer to solder wick and you need a lot of heat to pick up solder with wick
this one you have is not that flat though, its rounded, close enough but better look for similar one but with flat surface

zarbourne · 01-17-2017, 05:29

Quote:

Originally Posted by Kradziej

big, flat surface gives you proper and even heat transfer to solder wick and you need a lot of heat to pick up solder with wick
this one you have is not that flat though, its rounded, close enough but better look for similar one but with flat surface

I agree that tip is the best for picking up solder, but I disagree with using wick to pick up solder under big chips.

When Apple ship out their boards to production before components are installed, they have little solder on pads, not flat. Using wick can expose copper and hidden tracks!

Sent from my iPhone using Tapatalk Pro

01-16-2017, 04:47	#1 (permalink)
short_toground No Life Poster Join Date: Jul 2016 Posts: 536 Member: 2598526 Status: Offline Thanks Meter: 52	iPhone 6s PMIC keeps shorting Replaced PMIC twice and still it gets hot when connected to power with no boot, instant short circuit with bench power supply. Remove PMIC, short gone. Only there when installed. Any ideas?

01-16-2017, 18:52	#9 (permalink)
short_toground No Life Poster Join Date: Jul 2016 Posts: 536 Member: 2598526 Status: Offline Thanks Meter: 52	iPhone 6s PMIC keeps shorting What's the best tip to use for cleaning pads? I've been using this one Last edited by short_toground; 01-16-2017 at 19:26.

01-16-2017, 04:54	#2 (permalink)
zarbourne Freak Poster Join Date: Jul 2008 Location: Earth Posts: 171 Member: 813803 Status: Offline Thanks Meter: 120	Are you sure there is no short after you remove PMIC? Are you testing for short with DCPS or multimeter? You need to look on ZXW or Pads and see all the different lines/netnames that connect to PMIC and test for short with multimeter!

01-16-2017, 05:04	#4 (permalink)
zarbourne Freak Poster Join Date: Jul 2008 Location: Earth Posts: 171 Member: 813803 Status: Offline Thanks Meter: 120	ok thats good, when you clean solder of pads under pmic make sure that there isn't exposed lines, thats why I never use solderwick to clean solder I remove solder with the soldering iron and flux and leave small solder on pads, not flat! After that I put a little flux on pads so they help stick, then I align PMIC and push down (NOT TOO HARD!) and it is stuck. Then I look under microscope with board on angle so i can see if PMIC is aligned properly, then apple heat. That is perfect way in my opinion.

01-16-2017, 05:15	#6 (permalink)
zarbourne Freak Poster Join Date: Jul 2008 Location: Earth Posts: 171 Member: 813803 Status: Offline Thanks Meter: 120	Maybe, like in this picture you can see a track is a little exposed so sometimes solder can connect 2 pads after you put PMIC on. Hard for me to know where the short is without the phone infront of me.

01-16-2017, 05:17	#7 (permalink)
short_toground No Life Poster Join Date: Jul 2016 Posts: 536 Member: 2598526 Status: Offline Thanks Meter: 52	Oh ok I'll double check the pads

01-16-2017, 05:17	#8 (permalink)
zarbourne Freak Poster Join Date: Jul 2008 Location: Earth Posts: 171 Member: 813803 Status: Offline Thanks Meter: 120	Also, if you're reballing the pmic, and still short, then there is chance pmic is faulty, in which case put new one or one from other board

01-16-2017, 20:55	#10 (permalink)
Kradziej Freak Poster Join Date: Sep 2015 Posts: 198 Member: 2453408 Status: Offline Thanks Meter: 63	2nd visible from left but that looks like cheap chinese soldering iron so you are probably going to lift some pads with it be careful, dont slide over just press to the board

01-16-2017, 21:08	#11 (permalink)
short_toground No Life Poster Join Date: Jul 2016 Posts: 536 Member: 2598526 Status: Offline Thanks Meter: 52	So I'm testing the vcc_main points on the PCB with pmic removed and I measure multiple shorts to ground but if I measure vcc_main from another spot like a capacitor it doesn't read shorted. Only at the pmic pins

01-16-2017, 21:11	#12 (permalink)
Kradziej Freak Poster Join Date: Sep 2015 Posts: 198 Member: 2453408 Status: Offline Thanks Meter: 63	then you have incorrect schematics or you measure in incorrect places by mistake, there is no other way