Cheap way of mounting a BGA chip

See this old posting of mine here:

Now how in the hell are these companies going to make any money if they have to hold hands with every beginner that comes along.

You what to play, you have to pay. ( or get out of the business )

donald

Todays hobbyists are tomorrows customers. :-)

I've never done it before but is it possible to make a board where the edge pins of the BGA have a through-hole via to the other side of the board. I can then mount the chip by tacking the 4 corners through the via from the other side of the board. And then put the whole board in the oven to bake.

Is this practical at all? The bga pins already have solder on them do they not?

So why do you direct your reply at me - was it so hard to read before replying. I posted the solution, you see, not the question.

Didi

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Sorry

here:

If you have control over the manufacture of the board, the answer is yes. I've done just that on one-off samples for low budget in-house projects.

Thanks for the reply.

Is there anything beyond what I described that I should be doing to make sure the chip adheres? Should I perhaps be applying a small amount of (paste) flux to the underside of the chip so the solder melts at a lower temperature or is that unnecessary.

The BGA balls are all solder, actually. You have to stick the BGA with some flux - not liquid but not too hard either, I use a German one called "loethonig" (soldering honey... :-). Once stuck at its position, just reflow the board as I descrbed in my older posts and you are done (apart from washing). During reflow, the BGA floats on its liquid balls and gets properly positioned by surface tension. Be careful to stick it at the right place, it can be offset by a row... (once happened to me).

Didi

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Original message:

Hi Didi,

I did not understand what you meant about reflowing the BGA with belly up - could you explain again? Do you mean reflow the chips themselves (alone)?

Hi John,

yes, that's it - just the BGA alone. The reason is that some balls - I have had up to 2-3 per BGA - are "coldly" soldered to the BGA itself; so when the ball gets liquid and there is a hole underneath, it just flows throuh and the BGA pad gets completely disconnected. I don't know if all BGAs do it, but I have seen the effect on my first board with all 3 different sourced BGAs. Ever since I fry them once with flux belly up and have no issues, it does not take a lot to avoid cold soldering joints after all.

Didi

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Original message:

Interesting, thanks!

Just to get your opinion, what do you think of my method of tacking the 4 corners of the BGA with 4 through-hole vias and then putting it in the oven to bake (perhaps with a small lead weight positioned directly over the chip to force it down and keep it from sliding).

Do all BGA chips come with balls with solder already on them or just some?

I have not tried this but it does not sound like something which would have much of a chance to work. The first time I tried to solder the 3 BGAs on my first BGA board many years ago I stuck them in place with a UV hardening glue, just a drop every other corner or so. This fixed them well in place which was cute, but they did not have the chance to float and drop somewhat over the reflown balls so this was a complete failure. Expect something like that... :-). They do not slide so easily, just make sure to position the BGA in the right place (measuring from two board edges should be enough). Be very careful when you take the setup out of the oven; everything is liquid and if you knock it in some obstacle you are gone - *that* is when parts will slide (have had this as well, of course). If this happens, all you can do is to start all over after cleaning up the mess and reballing the BGA(s)...

They all come with balls *of* solder, not with. The entire balls are made of solder. Do not even think to put lead on top of the BGA, even if it does not melt to mess up the entire board the balls can take little more weight than the BGA itself while liquid.

Didi

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A large proportion of that is the cost of the stencil. Then there is the X-ray cost.

Leon

Such nonsense. What is he supposed to do with the stencil on a *BGA*? And what XRAY on Earth do you suggest for a prototype the guy wants to make? I have been doing BGAs for almost 10 years now and when I have used a stencil it has been for the parts other than the BGAs; I have never used XRAY.

Didi

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Original message:

These guys will do it for $50 each.

vorange schrieb:

cheers Gunther

Stencils are often used with BGAs for applying flux and solder paste.

Leon