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Ball Grid Arrays - DIY boards and soldering — Parallax Forums

Ball Grid Arrays - DIY boards and soldering

LoopyBytelooseLoopyByteloose Posts: 12,537
edited 2013-02-05 22:04 in General Discussion
I am wondering if anyone here has dared to fabricate boards and soldered ball grid arrays. I happen to be looking at a 16Mb SRAM chip that only comes in the this package and I am wondering if I am just a bit too wary about trying to build with these. It has a grid of 48 balls.

Since the balls are actual solder, I presume if I properly tinned the board - it might all go rather smoothly. Though I am wondering about having to solder mask a DIY board.

http://en.wikipedia.org/wiki/Ball_grid_array

Comments

  • WBA ConsultingWBA Consulting Posts: 2,934
    edited 2013-02-03 21:12
    You can actually solder a BGA straight to pads on a PCB without solderpaste on the pads as this is a typical method for rework. However, there are a few variables that can easily make the process a failure. First, the PCB pads need to be clean and flat. Theoretically, the coplanearity of the balls on the BGA will be very good, meaning that if you have any pads higher than others, the lower pads could end up with opens if the ball does not make contact with the pad during reflow. Also, you should apply a thin layer of a tacky rework flux to the PCB to aid in the balls adhering to the pads. Lastly, closely monitor your temperatures during reflow to ensure a proper solderjoint. The ball can collapse differently when solderpaste is not used which can create opens or fractured joints. Fractured joints can work fine at first, but under thermal stress will separate enough to create opens.

    This of course also depends on the type of BGA that you are using and how well you have the ball array lined up to the pads. What size is the BGA, what pitch are the balls, what is the ball diameter, and what alloy is it?
  • LoopyBytelooseLoopyByteloose Posts: 12,537
    edited 2013-02-05 05:18
    Thanks, I guess it is time for me to take a serious look at investing in hot air soldering equipment.

    Of course, good flux and everything clean are imperative.
  • prof_brainoprof_braino Posts: 4,313
    edited 2013-02-05 06:16
    Does one do this rework with a hot air solder station, or with a convection over? I've seen articles on both, but I don't know where each is used.
  • LoopyBytelooseLoopyByteloose Posts: 12,537
    edited 2013-02-05 08:45
    @PB
    That is a good question as I am thinking about soldering ball grid arrays and I suspect that using an oven is far better than other alternatives. So I suspect that I would have to adapt a toaster oven with an add-on control, maybe a microcontroller and thermal sensor to have the whole cycle kept within spec.

    Hot air is likely best for rework, not new construction. If one has to remove a ball grid array, the hot air would work. Then one has to rebuild the solder balls and go back into an oven to attach.
  • WBA ConsultingWBA Consulting Posts: 2,934
    edited 2013-02-05 09:23
    Most common for rework is hot air or IR. Rework equipment will have bottom heaters as well to balance the temperature across the board enough to prevent damage from localized heat at reflow temperatures. Since with BGAs you are heating through the part to reflow the balls, the part could be subjected to dangerous temperatures if your process is not controlled. In other words, lower temps at longer times is better than higher temps with shorter times. You need appropriate amounts of heat, but you need to "soak" that heat through the BGA slowly.

    Loopy, I have heard of people using a toaster oven to pull BGAs by reaching in with tweezers and lifting the part once it is fully above liquidus temp. Risky, but not impossible.
  • davejamesdavejames Posts: 4,047
    edited 2013-02-05 09:41
    Loopy Byteloose wrote: »
    I am wondering if anyone here has dared to fabricate boards and soldered ball grid arrays. I happen to be looking at a 16Mb SRAM chip that only comes in the this package and I am wondering if I am just a bit too wary about trying to build with these. It has a grid of 48 balls.

    Loop - this site may help with part of your dilemma:

    http://www.proto-advantage.com/store/index.php?cPath=4000&osCsid=b03ggmlj36niu9f3mruh2ce217
  • SRLMSRLM Posts: 5,045
    edited 2013-02-05 09:43
    I've been using a toaster oven and the Sparkfun hot air rework station for my SMD needs. I haven't done any BGAs yet, but I have done lots of small chips with hidden pins.

    Before I had the hot air rework station I had to use the method described by WBA to remove a chip. I'd heat up the whole board and, while hot, use tweezers to remove a part. I noticed that after 8 cycles or so that things started going bad. Plastic parts would change color, the board would make a cracking sound, and it just looked charred.

    So, now I use the hot air rework. It seems to work well.
  • frank freedmanfrank freedman Posts: 1,983
    edited 2013-02-05 22:04
    davejames wrote: »
    Loop - this site may help with part of your dilemma:

    http://www.proto-advantage.com/store/index.php?cPath=4000&osCsid=b03ggmlj36niu9f3mruh2ce217

    Can't speak to their ball product, but having used many of their other adapters, they work well. They don't protect you from yourself as well as the schmartboard though. As with schmartboard however, I wish they would use a smaller pin size to be easier on the breadboard sockets. Could also have used a full length pin because space for two level modified wrap just doesn't get it at times. Making the third level has no clean options.

    FF
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