Noob - reballing, balling, stencil questions...

[P Smith]

Re: Noob - reballing, balling, stencil questions...

update...
So i am practicing and made a couple of reballs ...first few were very bad...but getting better...
The question is regarding water damaged motherboards...i worked on two so far.. The problem is when i try to remove the water damaged chip...lets say cpu...it is partially corroded below because of water damage..and when i try to remove it will go out hard...and even then i pull out some pads from the board. I have to underlane that i use a lot of flux and hot air station is around 220 C, i never try to pull out chip by force...just a little touch to see if it is moving...And i should mention that on non corroded motherboards the removing of dead chip goes fine...
I believe the problem is in corroded pads...and probably because of corrosion they are pulled from the motherboard easily. I was thinking maybe if i increase temperature around 240 C maybe i could remove it more easily but i am afraid that i will damage/curve the motherboard that way.. ?
Have you any suggestions or ideas regarding topic?

I would try to rotate the chip by dental pic... without force !

[myth77]

Re: Noob - reballing, balling, stencil questions...

most likely to prevent water getting in between

OK, i investigate a little and it is not silicone...it is glue/epoxy that is put on corner of the bga chips to increase corner bond of the chip to the PCB. It is mechanical shock absorber, it promotes additional adhession to lessen stress to solder joints incase device subjected to mechanical stress like dropping. to prevent damage from falling laptop/motherboard or curved motherboard...

So, do you use it after replacing bga chips? and if yes what epoxy/glue do you use?

[myth77]

Re: Noob - reballing, balling, stencil questions...

Update, today i am really tired and pissed off...because of that shity epoxy that lenovo use. I spend a lot of time and nerves tried to clean that black shit from the bga and pch chip. When i replace chips on dead motherboard i usually prefer to use donor board other then to buy a new or used bga chip from china. Till now i had several asus and acer donor boards and it was not that hard to remove chip and clean it and reball it. Today i had for the first time lenovo donor board and boy i was suprised....First it is very difficult to remove chip from the board because of that epoxy and then you are in big trouble try to clean it...I think i will never use lenovo baord again for donor board...or i will never try to repair it if big chips are dead on it....its just to much trouble.
But maybe someone here has some tip on how to easily remove that black epoxy ?

[Spider1211]

Re: Noob - reballing, balling, stencil questions...

The edge bonding and underfill, as you mentioned is to provide mechanical stability/strength against drop etc. Most people don't usually replace the glue, but if you want to you could buy it (https://a.aliexpress.com/_mqS6gAb). You can also buy the underfill glue if you want, although I can't find link to it right now.

Can you upload pictures of the lenovo board/chip you mentioned? Whats the reference number?

[somes2121]

Re: Noob - reballing, balling, stencil questions...

I have the exact same problem as myth77, i use indirect stencils. The balls are washing away, i tried to use less flux, more flux, nearly no flux, bottom heat, bottom heat 107c+top heat with hot air station. What should i do? Last time i had few balls stuck toghether, i checked it before under microscope, everything was aligned.

[diif]

Re: Noob - reballing, balling, stencil questions...

I have the exact same problem as myth77, i use indirect stencils. The balls are washing away, i tried to use less flux, more flux, nearly no flux, bottom heat, bottom heat 107c+top heat with hot air station. What should i do? Last time i had few balls stuck toghether, i checked it before under microscope, everything was aligned.

Use next to no flux, just the tiniest bit to hold the balls in place, then use indirect heat, not hot air.