What size solder ball?

Thread Starter

Man_in_UK

Joined May 13, 2008
168
Sorry if this is not in the correct place.

I have never used solder balls before but need to replace a 96 pin Ball Grid Array package. The datasheet gives dimensions of 0.8mm pitch with 0.4mm balls.

If the pad is 0.4 ..... do I need 0.4mm balls?

Cheers
 

Thread Starter

Man_in_UK

Joined May 13, 2008
168
Have you searched on BGA reballing? Lots of art to it.
Here's a how to: https://www.instructables.com/Simple-BGA-Reballing/
I have seen it done and I know its not a two minute job. I am in a position where I have to attempt this to make a repair but I have not found any instruction or suggestion on ball size in relation to pad size.
The balls are easy to purchase but come in many different size!
 

jpanhalt

Joined Jan 18, 2008
11,088
I just posted an Instructable. That was not the only Google hit. Did you look at it? Did you try Google?

Moreover, Oshstencils is very knowledgeable. Have you contacted it?

Come on, you have to do something or whoever told you to get this done may be more than a little disappointed.
 

Thread Starter

Man_in_UK

Joined May 13, 2008
168
Come on, you have to do something
This 62 page document by AMD has got LOADS of information but all types of BGA, LGA,CGA etc but at no point does it suggest what size solder ball to use!
https://www.jlab.org/accel/eecad/pdf/044bgapackages.pdf

It does go into detail about solder paste but that does not help.

Google is usually quite good at coming up with answer to questions but not this time. I just wondered if anyone here has had any experience in the package I am using. Even the datasheet on he chip does not recommend anything.

I am making a repair on a faulty bit of audio equipment I own, I'm not in the business of repairing for customers.
 

jpanhalt

Joined Jan 18, 2008
11,088
How are you planning to attach your chosen size of solder balls to the pcb so you can reflow it? Do you understand the process? Maybe, I don't, but from what I have seen, "reballing" means reflowing solder paste, not actually placing individual solder balls of a specific size on the grid.
 

Thread Starter

Man_in_UK

Joined May 13, 2008
168
How are you planning to attach your chosen size of solder balls to the pcb so you can reflow it? Do you understand the process? Maybe, I don't, but from what I have seen, "reballing" means reflowing solder paste, not actually placing individual solder balls of a specific size on the grid.
I did not know that reballing means reflowing. All the reballing of BGA chips videos I have seen involves replacing the solder and the solder just happens to come in the shape of a ball.

The normal method would be to use a stencil but the device I have is only 12 x 12 and does not use all the pads. I have enough time to lay the balls out by hand under a magnifier, a thin layer of sticky flux should hold them in place long enough for me to flow them gently using a hot air station.
In the videos I have seen a lot of the people are using 0.5mm balls but they are working on much larger packages than the one I have here. I am worried that if I just guess the size and get it wrong, I run the risk of bridging a track.
 

jpanhalt

Joined Jan 18, 2008
11,088
Yes, balls can be used if the process is manual as you describe. I was thinking of a situation where you had to do more than one. As for missing connections (i.e., missing pads), one could easily use a stencil with the correct apertures. If the stencil was for all the pads, then it might be easier to print all and remove what's not needed. If you get a stencil made, then you could design it with only the apertures needed.

In the latter case, the stencil provider can provide advice. In the former case, I would ask the ball provider. As a guide, apertures for devices where shorts are likely to happen during reflow are often smaller than the pads by some percentage. I think Adafruit's video on using stencils suggests something on the order of 20% in each dimension. Moreover, as the solder paste melts, it usually gets smaller, so I would think that a solder ball should be smaller than the pad.

Solder paste that I use is 90% solder by weight. That is approximately 59% by volume (https://www.kester.com/Portals/0/Do...e/Calculating Solder Paste Volume Percent.pdf ). From that, the aperture size, and stencil thickness, one can calculate the volume of solder. Once you have that solder volume, you can calculate the ball diameter with the same volume. I do not know whether that is the correct diameter to use, but at least it is one approach.
 

ErnieM

Joined Apr 24, 2011
8,152
I did a bunch of these at one company where they packaged a hybrid circuit on a PCB, encapsulated it, but had no technique to get the balls attached.

What I did was first flood the base a thin layer of solder flux on the base. Then using tweezers I placed each ball over a pad. Finally I put it on the input side of our belt reflow machine, though any reflow device should work except hot air (which will blow the balls off target).

Surface tension will pull the vast majority of balls perfectly on center. The device I did had probably well over 100 pads and I might get one or two balls that wandered to another pad yeilding one double size ball and one empty pad. Easy enough to fix, solder wick up the bad ball and repeat flux and balls on the last few.
 

Thread Starter

Man_in_UK

Joined May 13, 2008
168
Did you use big balls or tiny ones? That is the question.
I have not purchased any yet as I still do not know what size i need.
Lucky for me, the chip is out of stock till March so I have some time to make my mind up. By the look of things I will probably get 0.5 and see how it goes.
 
Top