8
\$\begingroup\$

Consider an IC that looks like this, or similar:

enter image description here

Note how the leads that are soldered to the board are on the underside of the IC.

I am barely an electronics novice. My work with electronics is basically making simple repairs to old gaming hardware, so my expertise is very limited.

I've tried to google this but I must be mis-naming these components when I try to search for how this is done but how are components like these soldered onto boards in production units? I could easily see either these pins being coated in a bit of solder, or maybe a thin layer of solder is already on the PCB when the chip is placed on it. Regardless, how is each pin heated up to the proper temp so that the solder will melt and the chip will stick to the board?

I've tried to figure this out on my own, but so far this just seems like "black magic".

As a minor follow-up, if you are developing electronic hardware that needs a component like this, how do you use a chip like this in prototyping and testing? Is there a manual way to solder chips like this? Regardless of how it's done, it seems to me it'd at least have to be a mechanical process because you'd need a certain degree of precision.

\$\endgroup\$
  • 4
    \$\begingroup\$ They're "Ball Grid Arrays", usually BGA for short. \$\endgroup\$ – Finbarr Apr 5 '18 at 16:17
  • 1
    \$\begingroup\$ Key words and phrases to research: "BGA", "BGA fanout", "reflow oven", "solder paste", "solder paste stencil". Also, for working with BGA-only parts as a hobbyist, you may be able to find them already soldered to a break-out board or development board for prototyping. \$\endgroup\$ – Daniel Apr 5 '18 at 16:25
  • \$\begingroup\$ These seem like the bane of prototyping to me. \$\endgroup\$ – immibis Apr 6 '18 at 3:57
  • \$\begingroup\$ If you're interested in seeing this done in real time and with advice, go to YouTube and search "Loius Rossman BGA." They're long vids and you'll have to deal with his not always PC commentary, but he knows what he's doing. Multiple examples of chip replacement with a hot air station, solder paste stencil chip prep, and using a specialty BGA rework station for doing larger chips without having to reflow the entire board. \$\endgroup\$ – Phil C Apr 9 '18 at 4:33
28
\$\begingroup\$

This is a ball-grid array (BGA) package. Each little blob is actually solder. The component is placed precisely by a pick-and-place machine, and then the whole board is heated up to melt the solder (reflow soldering). The solder will flow to the pads on the PCB by surface tension, and the solder mask (hopefully!) stops it shorting out nearby pins. The advantage of the BGA package is the much greater pin density (and hence pin count) available compared to inline or QFN packages. You will typically find high pin count (FPGAs etc) components only available as BGA as it's impossible to bring out 1000 pins to the edges.

These are difficult to work with for prototyping work as it's nearly impossible to tell if the solder joint has been made. In mass production, this is done by X-ray imaging. You can make a reflow oven at home, but as you say the precise placement is quite tricky by hand, although not impossible.

Reworking is very difficult, you generally have to remove the whole component and reapply the solder blobs to remake it. Typically, vendors offer development boards with the BGA chip presoldered with the pins brought out to header pins, which are much easier to deal with.

\$\endgroup\$
  • 1
    \$\begingroup\$ Ah, thanks. This is what I was looking for in an answer. \$\endgroup\$ – RLH Apr 5 '18 at 16:46
  • \$\begingroup\$ And if soldering on both sides, there might be a blob of adhesive under the package to hold it on (particularly if it will be upside down in the reflow oven). \$\endgroup\$ – Jon Custer Apr 6 '18 at 1:46
7
\$\begingroup\$

You have a few questions in your post, and I think I can help with a couple of them.

Regardless, how is each pin heated up to the proper temp so that the solder will melt and the chip will stick to the board?

You need either a reflow oven, or if you're a hobbyist like myself you can get by using a hot air rework station. I have a rework station. It's basically a hair dryer that can get temperatures up to where solder melts. You wave the wand over the part, the part/board/solder gets hot enough, and the solder melts and does its magic.

Is there a manual way to solder chips like this?

Yes, there actually is! It takes practice and patience, but you don't need to send out to have this work done. It is possible to do it on your own. I do. This is the best video I can find that demonstrates the process. This is using a QFN (quad flat no-leads) not a BGA (ball grid array - the part you mention) but the idea is the same. The pins on the QFN are underneath the chip.

I've done this myself and it does work. And yes, it does seem a little like "black magic" when you do. But very satisfying!

\$\endgroup\$
  • 2
    \$\begingroup\$ Using solder flux is a big part of the "black magic", because dirty/oxidized contacts don't accept solder, and the surface tension of the melted flux helps align the package pins. \$\endgroup\$ – MarkU Apr 5 '18 at 22:55
  • 1
    \$\begingroup\$ @MarkU, yes that is absolutely correct. You need to clean the contacts and you need good flux or the magic won't happen. Check out that video clip I linked. There is a moment where the solder goes fluid, and the part the guy is soldering "pops" into place. He demonstrates the surface tension aspect by nudging the part. It doesn't want to move off the pins. The video was a real "aha" moment for me. I even started buying the flux the guy recommends. It's a great video. \$\endgroup\$ – BoredBsee Apr 6 '18 at 13:00

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.