What to do to NOT get popcorned chip.

[ktmmotocross]

Hello. I desolder GPU 7600go and it popcorned. the chip was shorted so i throw it to can. But what can i do to not popocorned it. temp of couple when desolder was 230c and was on the chip in the middle, so it wasnt a high temp. also i preheated board

[Th3_uN1Qu3]

Re: What to do to NOT get popcorned chip.

Popcorning happens due two 2 main causes. 1 is moisture trapped inside the chip, this can be dried by baking the board at 80-90C for a few hours. 2 is too aggressive top heater. What rework station do you have?

My personal preference is cranking the bottom heat high, even if it browns the board a bit. Just low enough that i don't get parts falling off. And do as little work with the top heat as possible.

[ktmmotocross]

Re: What to do to NOT get popcorned chip.

have home build station with adjust hight of top heater and bottom heater to be not agressive. my reflow time is 2x longer then optimal profile to be not agressive with temp rising

[Th3_uN1Qu3]

Re: What to do to NOT get popcorned chip.

Maybe your reflow time is actually too long. Exact data would help.

[dellxps15]

Re: What to do to NOT get popcorned chip.

do you use hot air top-bottom or full hybrid IR ?

i have full ir and if i stay at 225° on the chip for more then 30 seconds it will popcorn. ive seen that many people suggest to put (for a full ir) a kapton on the top of the bga to prevent popcorning.

baking and other operation are a bit too hard to do with normal staff (i dont have now a proper hooven)

[ktmmotocross]

Re: What to do to NOT get popcorned chip.

i have 200W halogen as bottom heater and 400W IR bulb as top heater.
top heater is pwm regulated and PID regulated

[tomodachi]

Re: What to do to NOT get popcorned chip.

I guess 7600 is already faulty from factory. my multiple reflows or reballs with this chip got popcorned annoyingly, especially the one at toshiba a100. you can find a new revision of that chip and it will be ok.

[Th3_uN1Qu3]

Re: What to do to NOT get popcorned chip.

i have 200W halogen as bottom heater and 400W IR bulb as top heater.
top heater is pwm regulated and PID regulated

There you go. You have too little bottom heat. 600-800W would be preferred. I have 800W, have modified a toaster with PWM control and it does the job. I don't think i've ever used more than 300W with the hot air on top.

And yes, more than 30 seconds above 220C will kill most chips. This is why i prefer to reball even new chips with leaded solder.

[ktmmotocross]

Re: What to do to NOT get popcorned chip.

my bottom is only 200W but can have no regulation and it preheat board to 150 in 9 minutes. i know it is slow but i think about preheat that slower is better. Or?

[sasser]

Re: What to do to NOT get popcorned chip.

Pre bake for reduce risk popcorned chip.

[dellxps15]

Re: What to do to NOT get popcorned chip.

my question is: if humidity (water)boil at 100° celsius, why popcorning generally happen only over 200° celsius?....
second: a very small quantity of humidity, shouldnt evaporate as soon as che chip reach a temperature of 120-150° ?

for me popcorning is just the too high temperature exposion like anso the unique sayd. generally if i reach 225° for 5 seconds, i never get popcorn.

[SteveNielsen]

Re: What to do to NOT get popcorned chip.

At a high enough temperature the water is probably expanding faster than the plastic case can let it out.

[claudyu07]

Re: What to do to NOT get popcorned chip.

I had same problem. Bake for 2 hrs at 100 degrees

[dellxps15]

Re: What to do to NOT get popcorned chip.

i did one today ( chip is 2010 )

note the kapton over the chip

[sasser]

Re: What to do to NOT get popcorned chip.

pre bake is take time consuming are kapton tape method can replace this procedure? and im worried when use kapton tape the tantalum cap on bga were melt too and maybe dislodged because kapton tape not sticky at high tempreture.

[Th3_uN1Qu3]

Re: What to do to NOT get popcorned chip.

I don't use tape of any kind over the chip and never had issues, but i'm using hot air.

The caps on top of the chip are ceramic not tantalum. They won't melt. If you accidentally move one or two off, they can always be put back in place with the hot air wand and appropriate nozzle. No problem.

[senndogg]

Re: What to do to NOT get popcorned chip.

I use a very-static self made station where bottom heating is the key. The small caps under the chip will never drop as they are already glued to the board. Just pay attention to not move your desk accidentally. i use a 600W halogen and usually i dont need to flow more than 2-3 minutes for removing the original 35x35mm chip with lead-free solder balls, and do not flow at all to chips with leaded solder balls as they will desolder very easy.
Unfortunately i havent had success with the big chips in the VGAs as 50x50, but
nowadays they are not worthy swapping as they cost more than a decent VGA.

I have found out that the notorious series of chips tend to popcorn most.

[ravi_1617]

Re: What to do to NOT get popcorned chip.

go to this website www.bgamods.com

[xboxhaxorz]

Re: What to do to NOT get popcorned chip.

the bottom of this article points out popcorning http://www.thebgareworkmachine.com/r...e-development/