Noob - reballing, balling, stencil questions...

[Spider1211]

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

Keep the stencils on and reduce the airflow. The stencil will help maintain the balls in place and lower airflow will avoid blowing the balls.

[myth77]

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

Are you using a heatgun or a hot air station? Are you removing the stencil before reflowing?

Yes i remove stencil before reflowing...and yes i use a heatgun but before that i preheat bga with small preheater to somewhere around 170C.

[Spider1211]

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

In my experience using only heatgun especially on large chips ends with balls moving on the chip before melting temeperature...but maybe i am doing something wrong.

Are you using a heatgun or a hot air station? Are you removing the stencil before reflowing?

[myth77]

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

Thank you for the answers...just a few more

2.) Baking should be around 125c.

For how long?

3.) I don't think there is a better way, just which ever way works, some like direct heat, others indirect or a bit of both. The less times the IC is subjected to reflow temperatures the better though.

In my experience using only heatgun especially on large chips ends with balls moving on the chip before melting temeperature...but maybe i am doing something wrong.

5.) There will be some colour change, I suggest using two thermocouples on the top to help with the accuracy of your temperature, it shouldn't need that hot with lead free balls.

ok, thank you..so you sugest lower top temperature...205C for 20 seconds on the end of the process?

[diif]

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

1.) Not every stencil is 100% accurate on the size.
2.) Baking should be around 125c.
3.) I don't think there is a better way, just which ever way works, some like direct heat, others indirect or a bit of both. The less times the IC is subjected to reflow temperatures the better though.
4.) The differing amounts are perhaps down to different fluxes ? I use the smallest amount possible otherwise there is a chance the balls can wash away if there is too much.
5.) There will be some colour change, I suggest using two thermocouples on the top to help with the accuracy of your temperature, it shouldn't need that hot with lead free balls.

[myth77]

Ok, like i said in the title i am new in bga replacing so i have a several questions:

1. Stencils...on every stencil it is written a size of a balls to use for reballing..but are they always correct? yesterday i was reballing one pch, on stencil it was written 0,45 mm...but i would swear that on other working board the balls were little smaller...maybe 0,4 mm
2. Trapped moisture...i read a lot of times that after and before replacing bga chips that they should be pre-baked for 8 houers on 52C...to dry any possible traces of trapped moisture...I just read about it a few times...but never seen on the videos on youtube anyone mentioned it in the process?
3. After i used stencil and put the balls on the bga it is better to use a small preheater, turn it on 170C and then after it reaches that temperature to use a hot air gun from top to solder balls?
4. When placing a chip back to the board before reballing with station...i should put a very small amount of flux? I am seeing videos on youtube and they are all different...on one video the guy is putting high amount of flux...and in the others only little from top of his finger...?
5. I tried to solder one pch yesterday (first try) with soldering station.... and pch from dark green colour has gone to very very dark green colour almost black..
I was careful with the temperatures... the bottom was never above 180C and upper was maybe for 20 seconds arround 220 C to reball it on the board...

Thank for the answers..