BGA non direct stencil help

[rtstorm]

Hi,

I need some help on reballing. I have 90x90 stencils. The problem is that not all balls wont go through the hole. Current i use 0.5mm stencil on some ATI radeon GPU.

When i put solder paste on IC and then put upper part od jig sometime the stencil is touching the ic and paste will stick on it

[Th3_uN1Qu3]

Re: BGA non direct stencil help

If you need to use that much flux paste that it gets in the holes of the stencil, you need to use better flux. What are you currently using?

[rtstorm]

Re: BGA non direct stencil help

I put a very thin layer or paste. I use amtech.

I notices that there is a 4 scree for adjusting height of distance upper part.

[Th3_uN1Qu3]

Re: BGA non direct stencil help

Genuine Amtech is good. That's what i use as well.

If you have height adjustment screws on your jig, try adjusting them so that the stencil comes ever so slightly above your chip, like 0.1mm or so. Look at an angle in powerful light and you should barely see a shadow under the stencil. Then try again and see if it's any better.

You need to get it far enough so that flux doesn't get into the holes of the stencil, but close enough for the balls to remain in place.

[nojgib]

Re: BGA non direct stencil help

Not sure how much flux you are using but a thin layer is key. If you have thick flux it will touch the stencil even with the jig set correctly.
Cleaning the flux from the holes can be a bit challenging but what worked best for me was alcohol based because it evaporates slower. Use a pin to gently poke any residue from the holes.

[rtstorm]

Re: BGA non direct stencil help

Thank you, i noticed that every time i put balls and when i try to lift stencil many balls stay on the stencils and wont fall through hole, like tha hole is to small but it is not.

[dellxps15]

Re: BGA non direct stencil help

put flux, then remove extra by passing 4 time (1 for each side) a similar " credit card" .

then put in place stencil and allign it perfectly. ofcourse before all that clean the stencil with a fresh isopropilic alchool.

edit: flux quality is very important. i use kingbo with pb or original amtech 559 uv tpf

[rtstorm]

Re: BGA non direct stencil help

Here is the picture of it. I dont know how but may ball stay in the stencil.

[nojgib]

Re: BGA non direct stencil help

It's hard to tell in the pic but I don't see any flux squishing though the holes so that's a good sign. If there is anything preventing the balls from falling onto the chip it would be easily seen by holding the stencil up to the light.

Thank you, i noticed that every time i put balls and when i try to lift stencil many balls stay on the stencils and wont fall through hole, like tha hole is to small but it is not.

The only other thing that comes to mind would be if the balls themselves have flux on them from previous attempts. I never put solder balls back into the container they came from because any slight residue of flux would make them stick together or stick on the stencil.

[stj]

Re: BGA non direct stencil help

cheap ultrasonic cleaner is handy for these problems.

[rtstorm]

Re: BGA non direct stencil help

Can i use the smaller ball? Like i have stencil that is 0.5 and i put ball 0.4?

I try again and still some ball left in stencil. I will try with new sets of ball because i put back sole ball after using them on stencil.

[dellxps15]

Re: BGA non direct stencil help

0.5, use 0.5 for ball that remain on stencil, or they were infected by some flux previously, or stencil is dirty of flux.

i clean always stencil each time with fresh isopropilic and balls that remain over the stencil i wont put back is solder balls contenitor, but will trow them for garbage.

[Beowulf]

Re: BGA non direct stencil help

You can get more help about bga rework on this forum
www.advancedreworks.com/forum

Yes it's perfectly fine to use smaller balls. But your problem is that your using too much flux. Start from putting almost nothing.

[harshad1975]

Re: BGA non direct stencil help

You can check my video on youtube .. it will help for direct heat stencil
reball process

watch this video :

http://youtu.be/0C80O7_galU

[BGA Rework Store]

Re: BGA non direct stencil help

think of a grain of rice put that amount on flux should be genuine if its amtech and got a holographic sticker (fake ) I dont sell fake amtech full of cheap crap , But if its orginal a grain of rice size and rub that all over the chip is more than enough, remember good flux is very tacky so little is best , also if you have been using alot of flux you may have clogged the holes on the stencil for stencils I sell the 9050 from aoyue drop those in job done , you can drop down .5 on solder balls but its down to flux and stencil use , dont panic when you look at the chip and think have i put enough on remember the job is to attach the solder and a nice shine of flux over the chip is all you need not a big wax look.
if you need stuff contact me and i will send you links Im U.K based but ship worldwide.