5 ms·

Any tips on getting started with FPGA on custom pcbs?

phendrenad2 8y ago
Power requirements are annoying. You need multiple voltages and they need to ramp up in a certain sequence at a certain ramp rate(!). Study reference designs - find a development board that has the same family of FPGA and also has published schematics and board layout (such as Intel and Xilinx official boards). Then just copy their power layout.
civilitty 8y ago
What exactly do you mean by "getting started with FPGA on custom PCBs?" Have you made custom PCBs with high density BGAs before? Most non-trivial FPGAs (to me that means you can easily fit a decent softcore processor with space left over for your FPGA logic) will be ball grid arrays and almost impossible to DIY without xray inspection equipment and a reflow oven. You can get what you need for a few hundred $ on eBay if you're patient and lucky but even then, getting to the point where you can solder the chips reliably will take time. If you have the budget for professional assembly, then I would start with a Digilent product that has an available reference design you can copy later. First get used to the FPGA and how it works (they are largely incomparable to a CPU or GPU except for the fact that they both have transistors). Then, design a simpler board with a smaller FPGA and work your way up to the big 500-1k pin chips.
- specialist 8y ago
  Aside: Have you ever considered a DIY youtube channel? If you, @slededit, others on this thread did something like Louis Rossmann, that'd be fantastic. I've never even seen a dentist's x-ray machine, much less seen it used for DIY design. That'd be amazing to watch. Louis Rossmann https://www.youtube.com/channel/UCl2mFZoRqjw_ELax4Yisf6w https://www.youtube.com/channel/UCl2mFZoRqjw_ELax4Yisf6w (But maybe y'all would dial down the rhetoric from an 11 to a 8 or 9.)
- slededit 8y ago
  You don't need XRay and your reflow oven can be a toaster oven. I do recommend a cheap microscope and a good pair of tweezers though. With this you can do 0.5mm pitch BGA although that is pushing it. I've made hundreds of prototypes this way. The fear of BGA parts is seriously overblown. The only real expensive part is the finer pitch parts will require tighter tolerances on the PCB which will take you out of the PCB batch services price tier. edit: toaster oven, not toaster
  - jacquesm 8y ago
    Your comment reads as if you equate 'BGA' with 'SMD', a BGA is a ball grid array with up to 1,000 tiny pads that have been pre-dipped in solder. Your toaster isn't going to work.
    - extrapickles 8y ago
      You can use a toaster, but your yield will be poor. Slapping some insulation on the oven and a PID controller will improve things significantly. If you screw up the solder job, you can use a hot air gun to remove the BGA part, reball it (using a stencil, fairly cheap if its a common package), then try reflowing again. If you practice for a few hours on scrap electronics, you can get good enough at it.
    - slededit 8y ago
      BGA is actually easier than leaded SMD parts. The tiny leads tend to bridge easily. With BGA you can be up to half the pitch off and it will center itself. I actually only go for leadless and BGA now because anything else is more of a hassle. It is a bit rude to assume I don't know what a BGA part is.
      - jacquesm 8y ago
        The tweezers bit is what triggered that. Handling a large BGA with tweezers is going to scratch the PCB if you're not ultra careful. Anyway, if you do this stuff often enough then I see no reason why you wouldn't get the proper tools, a rework station and an actual reflow oven or something with a PID controlled heating element would make your life so much easier. Working with bad tools would drive me nuts. The reason the larger BGA center themselves is as soon as the solder goes fluid there is a lot of accumulated surface tension trying to reduce the size of the bridge and that will center the part all by itself. For that to work properly though everything has to become fluid more or less at once and stay fluid until the part has shifted to the right position.
- mips_avatar 8y ago
  The project I'm working on right now is with a FLIR tau 2 thermal camera. Our university got it donated but the only decent expansion board is 1400 euro so i figured I might use that budget to build my own. I basically just need to convert LVDS to mipi csi-2 or ethernet. You can find the LVDS spec on page 16 of this spec sheet https://www.flir.com/globalassets/imported-assets/document/flir_tau_electrical_idd.pdf https://www.flir.com/globalassets/imported-assets/document/f... I need to make a board with the 50 pin hirose. Do you have any suggestions on getting started? I figured a qfp spartan 6 would be enough.
  - caraffle 8y ago
    Man I hate those connectors. I don't have a problem soldering most things down to 0.4mm pitch & 0402 components without magnification, but these connectors love to bridge. Either lay down a (thin!) bead of solder paste, or try drag soldering (I prefer this). With LVDS, make sure to keep tracks short,have some impedance control (doesn't need to be super strict), and match trace lengths. One issue I had before was a clock (90Mhz I think) that wasn't quite in sync. Ended up ordering a new board with a 8 channel inverter, and snaking the clock through a few of the the gates to get a slight delay.
  - bmcooley 8y ago
    I'm curious, my uni satellite club is using the same camera for a cubesat, is that the same domain you're using it for?
    - mips_avatar 8y ago
      We are building ours for a drone. Please feel free to contact me if you want to work together to figure this camera out.
moflome 8y ago
Just had a really good experience using a free online service [0] and using a home made reflow set up. I guess it depends on your end goals of the PCB deployment? [0] https://easyeda.com https://easyeda.com

Power requirements are annoying. You need multiple voltages and they need to ramp up in a certain sequence at a certain ramp rate(!). Study reference designs - find a development board that has the same family of FPGA and also has published schematics and board layout (such as Intel and Xilinx official boards). Then just copy their power layout.

civilitty 8y ago

What exactly do you mean by "getting started with FPGA on custom PCBs?" Have you made custom PCBs with high density BGAs before? Most non-trivial FPGAs (to me that means you can easily fit a decent softcore processor with space left over for your FPGA logic) will be ball grid arrays and almost impossible to DIY without xray inspection equipment and a reflow oven. You can get what you need for a few hundred $ on eBay if you're patient and lucky but even then, getting to the point where you can solder the chips reliably will take time. If you have the budget for professional assembly, then I would start with a Digilent product that has an available reference design you can copy later. First get used to the FPGA and how it works (they are largely incomparable to a CPU or GPU except for the fact that they both have transistors). Then, design a simpler board with a smaller FPGA and work your way up to the big 500-1k pin chips.

specialist 8y ago
Aside: Have you ever considered a DIY youtube channel? If you, @slededit, others on this thread did something like Louis Rossmann, that'd be fantastic. I've never even seen a dentist's x-ray machine, much less seen it used for DIY design. That'd be amazing to watch. Louis Rossmann https://www.youtube.com/channel/UCl2mFZoRqjw_ELax4Yisf6w https://www.youtube.com/channel/UCl2mFZoRqjw_ELax4Yisf6w (But maybe y'all would dial down the rhetoric from an 11 to a 8 or 9.)
slededit 8y ago
You don't need XRay and your reflow oven can be a toaster oven. I do recommend a cheap microscope and a good pair of tweezers though. With this you can do 0.5mm pitch BGA although that is pushing it. I've made hundreds of prototypes this way. The fear of BGA parts is seriously overblown. The only real expensive part is the finer pitch parts will require tighter tolerances on the PCB which will take you out of the PCB batch services price tier. edit: toaster oven, not toaster
- jacquesm 8y ago
  Your comment reads as if you equate 'BGA' with 'SMD', a BGA is a ball grid array with up to 1,000 tiny pads that have been pre-dipped in solder. Your toaster isn't going to work.
  - extrapickles 8y ago
    You can use a toaster, but your yield will be poor. Slapping some insulation on the oven and a PID controller will improve things significantly. If you screw up the solder job, you can use a hot air gun to remove the BGA part, reball it (using a stencil, fairly cheap if its a common package), then try reflowing again. If you practice for a few hours on scrap electronics, you can get good enough at it.
  - slededit 8y ago
    BGA is actually easier than leaded SMD parts. The tiny leads tend to bridge easily. With BGA you can be up to half the pitch off and it will center itself. I actually only go for leadless and BGA now because anything else is more of a hassle. It is a bit rude to assume I don't know what a BGA part is.
    - jacquesm 8y ago
      The tweezers bit is what triggered that. Handling a large BGA with tweezers is going to scratch the PCB if you're not ultra careful. Anyway, if you do this stuff often enough then I see no reason why you wouldn't get the proper tools, a rework station and an actual reflow oven or something with a PID controlled heating element would make your life so much easier. Working with bad tools would drive me nuts. The reason the larger BGA center themselves is as soon as the solder goes fluid there is a lot of accumulated surface tension trying to reduce the size of the bridge and that will center the part all by itself. For that to work properly though everything has to become fluid more or less at once and stay fluid until the part has shifted to the right position.
mips_avatar 8y ago
The project I'm working on right now is with a FLIR tau 2 thermal camera. Our university got it donated but the only decent expansion board is 1400 euro so i figured I might use that budget to build my own. I basically just need to convert LVDS to mipi csi-2 or ethernet. You can find the LVDS spec on page 16 of this spec sheet https://www.flir.com/globalassets/imported-assets/document/flir_tau_electrical_idd.pdf https://www.flir.com/globalassets/imported-assets/document/f... I need to make a board with the 50 pin hirose. Do you have any suggestions on getting started? I figured a qfp spartan 6 would be enough.
- caraffle 8y ago
  Man I hate those connectors. I don't have a problem soldering most things down to 0.4mm pitch & 0402 components without magnification, but these connectors love to bridge. Either lay down a (thin!) bead of solder paste, or try drag soldering (I prefer this). With LVDS, make sure to keep tracks short,have some impedance control (doesn't need to be super strict), and match trace lengths. One issue I had before was a clock (90Mhz I think) that wasn't quite in sync. Ended up ordering a new board with a 8 channel inverter, and snaking the clock through a few of the the gates to get a slight delay.
- bmcooley 8y ago
  I'm curious, my uni satellite club is using the same camera for a cubesat, is that the same domain you're using it for?
  - mips_avatar 8y ago
    We are building ours for a drone. Please feel free to contact me if you want to work together to figure this camera out.

moflome 8y ago

Just had a really good experience using a free online service [0] and using a home made reflow set up. I guess it depends on your end goals of the PCB deployment? [0] https://easyeda.com https://easyeda.com