On Fri, 13 Jan 2023 21:20:50 -0800 (PST), "gnuarm.del...@gmail.com
>On Saturday, January 14, 2023 at 12:39:49 AM UTC-4, John Larkin wrote:
>> On Sat, 7 Jan 2023 09:49:24 -0800 (PST), "gnuarm.del...@gmail.com
>> >A small board with a 100QFP is being redesigned for a new FPGA due to obsolescence. Gowin makes a 100QFP device that would be a good fit, but my customer has said "no" to the 100% Chinese brand... US government customers, ya know!
>> >So now I'm looking at a BGA. I don't want to get into fine PCB design rules, so 1.0 mm ball pitch is my preference. The only devices I can find that fit on the board have 196 or 256 pins. But the real problem is availability.
>> >Digikey has a few of the XC7S15-1FTGB196I and more a scheduled for delivery in April. Add in the various speed and temperature flavors trickling in (mostly in April) and I should be ok for the initial delivery in August... if I can get my hands on those. I don't know if Digikey factors in the backlog orders in these counts.
>> >Mouser shows great inventory of Efinix parts, particularly the T13 and T20 in a 0.8 mm 256 pin BGA, 10s of thousands in stock. But I'd rather work with a 1.0 mm BGA. Oddly enough, LCSC shows part numbers, but zero inventory.
>> >Anyone work with 0.8 mm BGAs? What PWB feature dimensions did you use? Did this impact the PWB cost?
>> The 0.8 mm 256-ball T20 isn't bad...
>I can't really see much detail. It looks like there are virtually no pads on the vias under the BGA. What size are they?
The BGAVIAs are 12.5 mil OD with 8 mil drills. The other vias on the
board STANDARDVIA and POWERVIA are bigger.
I have seen vias with no annullar ring, just a trace falling into a
hole, but the PCB houses don't like that.
Filled via-in-pad would be cool but that's complex and expensive. As
is buried vias.
>> The BGA pads are 16 mils. 8 mil drills on the BGA vias. 6 mil traces
>> mostly, except for the 50 ohm monsters. No big deal these days. Works
>Yeah, 0.8 mm pad centers are doable, but I don't know where the line is for higher pricing on the PWB. The via pads seem to be pushing the technology line at JLCPCB. Not that I'm using them, but if they can do it, pretty much anyone should be able to do it. They build 0.45 mm via pads and 0.2 mm drills (5 mil annular ring and 8 mil drill), but charge extra for a 0.4 mm via pads (4 mil annular ring).
We use US suppliers for production boards, and they seem to think this
6-layer board is within the normal range. One advantage to using a big
FPGA (256 balls in this case) is that you don't have to go deep to hit
enough balls, so may save a PCB layer or two. The T20-256 is a nice
part and Digikey has 29,000 in stock.
Another project used a 484 ball Zynq and we used almost every ball.
Lots of different power pours too. That took 10 layers. Another recent
board has a 400-ball ZYNQ with a few unused PS pins and fits on 8
The ZYNQ has analog inputs but, crazily, they are all differential so
they make you ground a perfectly good i/o pin for every analog input
that you want.
>> We considered a T8 for a simpler application, but its 0.5 mm ball
>> pitch looked nasty.
>I didn't price the T8, because they use the logic cells for routing in a way they don't explain, so no way to factor it in. The T12 would be gravy for my design I expect, but it's only $1 more for the T20, so why not? If it saves a day of work, it's a break even for 1,000 units. If it enables a future expansion, it's worth much more than that! Both parts seem to have the same pin out, including I/O counts, so switching between them should only be a recompile.
>> The efinix tool chain looks like it was developed in someone's garage,
>> which is actually praise. It's free and simple and just works without
>> 200 gbyte downloads and doing battle with FlexLM.
>The large downloads are from the support for the many, many products the big three FPGA companies sell. Don't expect Efinix tools to continue to be small... and they aren't really free. You have to buy a board. That's more than I've paid for tools from FPGA vendors.
$150! That's in the noise, and an eval board is good anyhow.
>I'd really like to use the Gowin parts (LQFP100). But the customer is hinky about parts from a Chinese company. They sell stuff to the US Government.
Yeah, we have a lot of aerospace customers and avoid Chinese parts.