Hi,

I am about to do my first PCB including a BGA chip. I have some decent soldering skills with the iron, as well as with the air gun, but I have never done BGA one... My chip is the TFBGA100 with the pitch of 0.8mm. The chips that I have bought seem to already have some kind of (most probably) solder bubbles on them (pictures of the chips included, I have not touched anything...) So my question is what is the best/most common way to solder the BGA?

1) To clear the pads from solder as good as possible and use a stencil with the solder paste every time (for that small section of your PCB)?

2) To apply some solder on the pads, some clean-free liquid flux, put the chip on top, blow the air until you feel like it has soldered already and hope for the best?

3) In my case (with the assumption that the chip has some solder on the pads of the chip itself already) just put a chip on the PCB and solder with hot air gun?

4) Any other method?

Of course, this is not going to be the mass production, just for my own projects... Another question. As the name BGA implies, the chips have actual conductor balls making up the electrical connection. I have seen some BGA balls for sale on Ali and other sites. So what exactly is a BGA ball? Is it a separate physical ball that is preserving its shape by the time of soldering (is it a non-melting conductor ball surrounded by solder from both sides)? Or is it just a small solder ball (just some tiny amount of actual solder that got the name ,,ball" because of its shape when melted on a very small round pad.) If its the second case, what is the point to sell bottles of lets say 100g of ,,0.5 mm pitch BGA balls" consisting of ,,billions" of solder balls? I hope I explained my questions well enough, thank you. Any other tips on BGA soldering are really appreciated.

 

I'm not sure if a hot air gun would work on BGA. If you have spares, you could certainly try, but the most reliable way to do BGA is with some form of reflow oven (which are specifically designed with temperature rampup and cooldown to optimize bonding). Basically, you need to uniformly (or, as uniformly as possible) heat the entire BGA chip simultaneously so all the balls melt, so the chip won't tilt or drift.

For BGA, do not apply solder paste to the pads: the balls are, themselves, solder, and are "calibrated" to be exactly enough solder to form a good joint and to prevent excessive flowing (as the surface tension of the molten solder will wick the chip into place). I've heard that a toaster oven might work as a reflow oven, but that's a bit risky (contamination, temperature too high/too low, lack of control, etc). Just align the chip and apply heat carefully, and it should flow into place.

You could also get a hotplate and, very, very carefully, use your hot-air gun to do BGA soldering as well. See this link for an example.

To answer your questions there at the end, a BGA "ball" is simply a ball of solder (of varying size and pitch) that is, somehow, attached to the chip which it is supposed to mount ("how" depends on the process). For a hobbyist there's probably no point in purchasing a bottle of just the balls, unless you plan to do BGA re-balling, which has its uses.

Good luck! Hope this helps.

 

I'm not sure if a hot air gun would work on BGA. If you have spares, you could certainly try, but the most reliable way to do BGA is with some form of reflow oven (which are specifically designed with temperature rampup and cooldown to optimize bonding). Basically, you need to uniformly (or, as uniformly as possible) heat the entire BGA chip simultaneously so all the balls melt, so the chip won't tilt or drift.

For BGA, do not apply solder paste to the pads: the balls are, themselves, solder, and are "calibrated" to be exactly enough solder to form a good joint and to prevent excessive flowing (as the surface tension of the molten solder will wick the chip into place). I've heard that a toaster oven might work as a reflow oven, but that's a bit risky (contamination, temperature too high/too low, lack of control, etc). Just align the chip and apply heat carefully, and it should flow into place.

You could also get a hotplate and, very, very carefully, use your hot-air gun to do BGA soldering as well. See this link for an example.

To answer your questions there at the end, a BGA "ball" is simply a ball of solder (of varying size and pitch) that is, somehow, attached to the chip which it is supposed to mount ("how" depends on the process). For a hobbyist there's probably no point in purchasing a bottle of just the balls, unless you plan to do BGA re-balling, which has its uses.

Good luck! Hope this helps.

So what happens (what should the one do) if you want to unsolder and solder your BGA chip again on different PCB or in other case... Some portion (possibly even a large portion) of solder on the BGA will be left on the PCB inevitably. Do you try to add the solder to the BGA manually?

I have a PCB heating plate, but there are situations when you are not doing an assembly for whole PCB, lets say you are just un/soldering the BGA. Do I really have to use the plate (there may be some plastic connectors, or some heavy components on the other side of the PCB)? Why I can not use just the air gun?

 

Why I can not use just the air gun?

You can't ensure that all of the solder balls will melt. There is yield loss even when you use the correct equipment.

A hot plate might work for assembly, but reworking a board requires expensive equipment.

 

I'm not sure if a hot air gun would work on BGA. If you have spares, you could certainly try, but the most reliable way to do BGA is with some form of reflow oven (which are specifically designed with temperature rampup and cooldown to optimize bonding). Basically, you need to uniformly (or, as uniformly as possible) heat the entire BGA chip simultaneously so all the balls melt, so the chip won't tilt or drift.

For BGA, do not apply solder paste to the pads: the balls are, themselves, solder, and are "calibrated" to be exactly enough solder to form a good joint and to prevent excessive flowing (as the surface tension of the molten solder will wick the chip into place). I've heard that a toaster oven might work as a reflow oven, but that's a bit risky (contamination, temperature too high/too low, lack of control, etc). Just align the chip and apply heat carefully, and it should flow into place.

You could also get a hotplate and, very, very carefully, use your hot-air gun to do BGA soldering as well. See this link for an example.

To answer your questions there at the end, a BGA "ball" is simply a ball of solder (of varying size and pitch) that is, somehow, attached to the chip which it is supposed to mount ("how" depends on the process). For a hobbyist there's probably no point in purchasing a bottle of just the balls, unless you plan to do BGA re-balling, which has its uses.

Good luck! Hope this helps.

Interesting information. That brings up a question. I was also considering using BGA's on future boards. The company I work with also makes stencils for the board. In this case you have to somehow inform the maker of the stencil that the BGA pads are not to exist on the stencil. I am using KiCad, not sure how you tell the tool that information in order to make a stencil that does not have the BGA pads exposed.

 

You can't ensure that all of the solder balls will melt. There is yield loss even when you use the correct equipment.

A hot plate might work for assembly, but reworking a board requires expensive equipment.

,,but reworking a board requires expensive equipment"

Can you tell more? What kind of equipment?

 

What kind of equipment?

Something like this:

https://www.pcb-repair.com/bga-rework-station/

 

Interesting information. That brings up a question. I was also considering using BGA's on future boards. The company I work with also makes stencils for the board. In this case you have to somehow inform the maker of the stencil that the BGA pads are not to exist on the stencil. I am using KiCad, not sure how you tell the tool that information in order to make a stencil that does not have the BGA pads exposed.

I know in certain tools you can specify what layers go to which GRB file, so you could put a kind of "mask" over the BGA footprints on some annotation layer and incorporate it into the appropriate layer. However, I'm not sure how you'd do it in KiCAD, as it has its layer manager pretty locked down (if I recall right) when it comes to creating the manufacturer outputs. I'd have to look into that myself.

Something like this:
View attachment 293118
https://www.pcb-repair.com/bga-rework-station/

Precisely stations like this. In regards to reflow ovens, there's usually a reason that PCB fabs or board shops have someone specifically trained up to work a reflow or rework station, considering how touchy and finicky they can be (and many may have an X-ray machine to go with it to make sure everything is intact or attached correctly). Where I work there's an entire section of a board shop that focuses on this kind of stuff (conveniently associated with failure analysis lab).

So what happens (what should the one do) if you want to unsolder and solder your BGA chip again on different PCB or in other case... Some portion (possibly even a large portion) of solder on the BGA will be left on the PCB inevitably. Do you try to add the solder to the BGA manually?

You would have to re-attach the balls yourself in some fashion, probably through the use of the rework station. Re-balling BGA chips can be challenging, and there's a few ways they do it, but I'm definitely no expert on that.

 

I know in certain tools you can specify what layers go to which GRB file, so you could put a kind of "mask" over the BGA footprints on some annotation layer and incorporate it into the appropriate layer. However, I'm not sure how you'd do it in KiCAD, as it has its layer manager pretty locked down (if I recall right) when it comes to creating the manufacturer outputs. I'd have to look into that myself.



Precisely stations like this. In regards to reflow ovens, there's usually a reason that PCB fabs or board shops have someone specifically trained up to work a reflow or rework station, considering how touchy and finicky they can be (and many may have an X-ray machine to go with it to make sure everything is intact or attached correctly). Where I work there's an entire section of a board shop that focuses on this kind of stuff (conveniently associated with failure analysis lab).



You would have to re-attach the balls yourself in some fashion, probably through the use of the rework station. Re-balling BGA chips can be challenging, and there's a few ways they do it, but I'm definitely no expert on that.

I understand that this is not for commercial use by any means, but for home lab experiments: what if I put a stencil (same stencil designed for the PCB footprint) on top of the BGA chip and applied the paste to the chip, then after stencil removal I would use the air gun to form the balls on the BGA, does this at least see a chance of working?

 

I know in certain tools you can specify what layers go to which GRB file, so you could put a kind of "mask" over the BGA footprints on some annotation layer and incorporate it into the appropriate layer. However, I'm not sure how you'd do it in KiCAD, as it has its layer manager pretty locked down (if I recall right) when it comes to creating the manufacturer outputs. I'd have to look into that myself.



Precisely stations like this. In regards to reflow ovens, there's usually a reason that PCB fabs or board shops have someone specifically trained up to work a reflow or rework station, considering how touchy and finicky they can be (and many may have an X-ray machine to go with it to make sure everything is intact or attached correctly). Where I work there's an entire section of a board shop that focuses on this kind of stuff (conveniently associated with failure analysis lab).



You would have to re-attach the balls yourself in some fashion, probably through the use of the rework station. Re-balling BGA chips can be challenging, and there's a few ways they do it, but I'm definitely no expert on that.

Thanks for the advice. I think I found a way to turn off solder paste for a given pad in the part design tool:


It appears all you have to do is uncheck 'F.Paste' on the technical layers. I will test that and verify the stencil should have it removed then. Thanks!

 

I understand that this is not for commercial use by any means, but for home lab experiments: what if I put a stencil (same stencil designed for the PCB footprint) on top of the BGA chip and applied the paste to the chip, then after stencil removal I would use the air gun to form the balls on the BGA, does this at least see a chance of working?

It might; depends on the pitch (if the BGA chip itself has lost its solder balls). The only way to find out is to try, I suppose (if you have some you can experiment on, that is). If the pitch is too narrow, then the balls may not form right (or may overflow), or the bond may not form right, but, for personal/hobbyist use, it might work, maybe.