4 ms·

You can even run 4-layer impedance controlled boards that support BGAs for ~$60 and get 10 of them. Problem is I now have a bunch of unpopulated PCBs I don't re

You can even run 4-layer impedance controlled boards that support BGAs for ~$60 and get 10 of them. Problem is I now have a bunch of unpopulated PCBs I don't really intend to use. I made a few PCIe x1 to SMA adapters for an FPGA devkit - even building a single one and considering the rest of the PCBs as write-offs was less than a quarter the price of premade ones.

aidenn0 5y ago
Can you verify good flow of solder on a BGA without an x-ray? Do you just reflow it for the prescribed time and see if it works?
- antoinealb 5y ago
  It is already the way you do it for parts like QFN (at least the way I do it): if it works then all good! If it does not, then heat it up again. I heard BGA is actually pretty simple as you cannot apply too much paste, but I don't have so experience with it.
  - Teknoman117 5y ago
    I'm doing this as a test mostly. I bought some 0.8mm 121 pin lattice iCE40HX FPGAs ($5 a pop) to test with with. Few enough balls that you can do a 4 layer stackup without cheating (no traces in the power plane layers). I hand-placed some 0.4mm QFNs before (LVDS to TMDS converter IC) (admittedly, only a ~90% success rate) so this has to be at least twice as easy.
    - aidenn0 5y ago
      "Easier than QFN" isn't a glowing recommendation but makes me hopeful. QFNs are the bane of my existence.
      - Teknoman117 5y ago
        I should mention, when I did QFNs, I used solder paste, a stencil, and a hotplate. I don't think I could ever manage to hand solder one. Passives on the backside were done with solder paste, a stencil, and a hot air reflow station.
        antoinealb 5y ago
        Do you have a reference to a hotplate you like for QFN? I have been considering one because I just don't get good results with hot air, and a reflow oven seems like a bit too much for my use case.
- fest 5y ago
  If the board layout permits it, you can inspect the outside balls around the perimeter- if they are fine, the inside ones will most likely be fine as well. Sometimes, a small piece of front-surface mirror can be used to inspect the sides of the chip obscured by taller components. Even PCBA companies usually just place and reflow the chip and may only use x-ray to validate the initial build- and then rely on process consistance + functional testing at the end of line.

aidenn0 5y ago

Can you verify good flow of solder on a BGA without an x-ray? Do you just reflow it for the prescribed time and see if it works?

antoinealb 5y ago
It is already the way you do it for parts like QFN (at least the way I do it): if it works then all good! If it does not, then heat it up again. I heard BGA is actually pretty simple as you cannot apply too much paste, but I don't have so experience with it.
- Teknoman117 5y ago
  I'm doing this as a test mostly. I bought some 0.8mm 121 pin lattice iCE40HX FPGAs ($5 a pop) to test with with. Few enough balls that you can do a 4 layer stackup without cheating (no traces in the power plane layers). I hand-placed some 0.4mm QFNs before (LVDS to TMDS converter IC) (admittedly, only a ~90% success rate) so this has to be at least twice as easy.
  - aidenn0 5y ago
    "Easier than QFN" isn't a glowing recommendation but makes me hopeful. QFNs are the bane of my existence.
    - Teknoman117 5y ago
      I should mention, when I did QFNs, I used solder paste, a stencil, and a hotplate. I don't think I could ever manage to hand solder one. Passives on the backside were done with solder paste, a stencil, and a hot air reflow station.
      - antoinealb 5y ago
        Do you have a reference to a hotplate you like for QFN? I have been considering one because I just don't get good results with hot air, and a reflow oven seems like a bit too much for my use case.
fest 5y ago
If the board layout permits it, you can inspect the outside balls around the perimeter- if they are fine, the inside ones will most likely be fine as well. Sometimes, a small piece of front-surface mirror can be used to inspect the sides of the chip obscured by taller components. Even PCBA companies usually just place and reflow the chip and may only use x-ray to validate the initial build- and then rely on process consistance + functional testing at the end of line.