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Hand soldering BGA wafer chips

hand-soldering-bga-chips

And here we’ve been complaining about Flat Pack No-Lead chips when this guy is prototyping with Ball Grid Array in a Wafer-Level Chip Scale Package (WLCSP). Haven’t heard that acronym before? Neither had we. It means you get the silicon wafer without a plastic housing in order to save space in your design. Want to use that on a breadboard. You’re crazy!

Eh, that’s just a knee jerk reaction. The wafer-level isn’t that unorthodox as far as manufacturing goes. It’s something like chip on board electronics which have that black blob of epoxy sealing them after the connections are made. This image shows those connections which use magnet wire on a DIP breakout board. [Jason] used epoxy to glue the wafer down before grabbing his iron. It took 90 minutes to solder the nine connections, but his second attempt cut that process down to just 20. After a round of testing he used more epoxy to completely encase the chip and wires.

It works for parts with low pin-counts. But add one row/column and you’re talking about making sixteen perfect connections instead of just nine.

Comments

  1. DainBramage1991 says:

    I guess some people have steadier hands than I do. I would end up with all six wires and the chip encased in a large blob of solder if I tried something like that.

  2. Matt says:

    this kind of assembly would lend itself well to a simple CNC machine, like a soldering iron tip on a gantry made out of CD drive sleds and steppers. If you were doing 16 or 25 pins and up it would be worthwhile.

    • Steve says:

      That’s exactly what a wire bond machine does.

      • jonam says:

        For my EE thesis in 1985, I had to use a manual wire bonding machine to connect my unpackaged test chip to a PCB. It was quite hard to do even with the aid of a microscope so I’m astounded that someone has attempted soldering. Fantastic!

        • Sven says:

          He hasn’t bonded to the chip, it’s a “flip chip”, a die with the connection points bonded to solder pads on the back.

          It’s basically an extremely small BGA without a plastic package.

  3. Andrew F. says:

    Why not just reflow this? Am I missing something? Especially for larger arrays, I couldn’t imagine doing this without a hotplate.

  4. Xevel says:

    That’s nice.

  5. I won’t say that it’s easy, but that’s not *so* hard, the technique was demonstrated a few months ago on HaD with another bga hand soldering (a texas instruments optical sensor, IIRC).

    The trick is to heat the magnet wire, not the solder ball. The heat conduction is enough to melt the ball through the wire.

    This way, the soldering tip never touches the package, and you don’t have any risk to mess the already-soldered wires.

    Obviously, gluing the chip before anything is more than useful.

    • RP says:

      “The trick is to heat the magnet wire, not the solder ball.”

      That makes me wonder if a technique could be developed using a length of wire heated electrically (resistance heating) so no iron would be needed at all.

      Perhaps form the wire into a hairpin like a soldering iron tip and then either use both legs to make the board connection or cut one off afterward. Alternatively you could stretch the wire across 2 solder balls, cut in the middle and have 2 lags at once.

      • ginbot86 says:

        It could work but it’d likely be too much hassle to get working consistently. The current going through the wire would have to be just right to be able to melt the solder but not so hot that it becomes incandescent; otherwise the wire would just oxidize and won’t stick to the solder ball.

        That said, if I have time I might give it a go and see if it works out.

  6. jh says:

    I’ve dealt with failure analysis of these types at work… lets just say that I have to use microprobes to deal with these. I’ve got some steady hands, but still not good enough to solder wires to these little bastages. Though, the folks down the hall that do reball, might.

  7. Taras Anatsko says:
  8. ion says:

    What are the material of balls. Is it solder ? It will melt on the oven? If it is solder, and the pcb is gold plated or solder platted , do i need to apply solder paste, or just flux?
    Can i put just flux, place the chip and pot it in the infrared oven for reflow soldering ?
    Or i need to apply solder paste like i do with regular smd components. I have a very good and reliable solder oven and i can program the solder curve on it.
    I need to do some experiments, and the only components i find are BGA, small pin counts, 16 the most.
    Thank you

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