Making A PGA Chip Like PCB Module - Page 1
Forum section: electronics / general

author: sobakava
author_rank: Contributor
timestamp: October 03, 2022, 01:38:08 pm
content: Hello Everyone,I made a PCB as a breakout board to a BGA IC. Around the IC, I've some passive components, crystal, inductor etc. I wanted it to be used with a PGA socket just for convenience. I've 60 pins total, 57 is the minimum possible.I am using both sides of the PCB for these components.Initially I used 2.54mm pitch standard male dual-row pins shown as below. The outline is 10x9, not a square.My pin configuration is shown below, I have 60 pins in total with some redundant pins, I can go down to 57.So for the next revision I am considering to use 9x9 outline to make it square, with a 1 pin placed at inside:I found some vendors manufacturing custom PGA sockets. Even with male-male pins shown as below (left),For the carrier (main) board, user can use a PGA female socket or directly solder to the PCBAlso the overall stack-up height is reduced.Anyway, I was thinking about my other/better options.I realized that some of the custom socket manufacturers are actually making some sort of FR4 PCB as a socket adapter:So I started to think about having these pins directly on my PCB.I checked Digikey to find pins like shown above, but I am not sure which pin to order. Having combined pins would be nicer.Also I am afraid, having individual pins assembled may be problematic for the assembly house.And of course total number of pins is 57; even at 20cent/pin price ends up at a very high total cost...What do you suggest for this kind of breakout board?I want to make this breakout board :- manufacturable- not costly- easy to use by hobbyists without needing too much soldering skills- both directly soldering and a low-cost socket compatible

author: nctnico
author_rank: Super Contributor
timestamp: October 03, 2022, 08:14:03 pm
content: Nowadays I'd go for castellated holes:

author: thm_w
author_rank: Super Contributor
timestamp: October 03, 2022, 10:02:52 pm
content: If you have control over the base PCB with the connectors, and you want 0.1" pitch, whats wrong with the dual row male pins and sockets? Its likely going to be the cheapest option.Machined pins are nicer, but much more expensive (~5-10x). Up to you if its worth the cost.You can do SMD headers as well. And I would get rid of that third pin, if its possible to find another way to orient the socket that doesn't require soldering in a single pin.Quote from: nctnico on October 03, 2022, 08:14:03 pmGood idea, although 60 pin castellations that are easy to solder will be fair bit larger than the existing design.

author: Zoli
author_rank: Frequent Contributor
timestamp: October 04, 2022, 03:17:02 am
content: Quote from: sobakava on October 03, 2022, 01:38:08 pm20 gold plated 0.5mm pins for less then $1:https://lcsc.com/product-detail/Pin-Headers_XKB-Connectivity-X5521WV-2X10-C46D46-1220_C2764589.html8 gold plated 0.5mm pins for less then $0.5:https://lcsc.com/product-detail/Pin-Headers_XKB-Connectivity-X5521WV-2X04-C40D40-1196_C2764592.htmlOverall less then $5; oh, and you're welcomeEdit: typos

author: sobakava
author_rank: Contributor
timestamp: October 04, 2022, 02:47:14 pm
content: Yeah this looks interesting. Thank you!I think I can use 2pc 2x9 and 2pc 2x5 connectors, so I can have a dual row 9x9 square.There are multiple partshttps://lcsc.com/product-detail/Pin-Headers_XKB-Connectivity-X5521WV-2X05-C35D35-1000_C2764571.htmlhttps://lcsc.com/product-detail/Pin-Headers_XKB-Connectivity-X5521WV-2X05-C40D40-1196_C2764593.htmlhttps://lcsc.com/product-detail/Pin-Headers_XKB-Connectivity-X5521WV-2X05-C46D46-1220_C2764586.htmlApart from mated height, what is the difference? Are they all suitable for soldering to a PCB to make it like a PGA chip?Thanks

author: sobakava
author_rank: Contributor
timestamp: October 04, 2022, 03:04:41 pm
content: Quote from: nctnico on October 03, 2022, 08:14:03 pmI actually thought about this but I want this module to be used with a socket as well. Also as thm_w mentioned above, it makes the board much much bigger compared to 2 row connectors at each side.

author: Zoli
author_rank: Frequent Contributor
timestamp: October 04, 2022, 03:23:33 pm
content: Quote from: sobakava on October 04, 2022, 02:47:14 pmThey're gold plated, so they should be suitable for attaching to PCB; but since they're not that expensive, I think you should order some samples to check which is suitable for your application.One more thing you should pay attention: holes. Since the pins are 0.5mm, the PCB holes should be in the 0.6-0.8mm range.

author: nctnico
author_rank: Super Contributor
timestamp: October 04, 2022, 09:24:44 pm
content: Quote from: sobakava on October 04, 2022, 03:04:41 pmYou can make the board square and use a finer pitch of castellated pins. A 1.27mm pitch for example. With 19 pins on each side of a 25x25mm PCB you get to 76 pins in total. With a finer pitch, I'd use a thinner board though (like 1mm thick). You could provide a seperate breakout board that connects to 2 rows of header pins for people that want to experiment. Having all connections in a row will be more conventient compared to a square array anyway.