Trying out via-in-a-pad at JLCPCB - Page 1
Forum section: electronics / general

author: asmi
author_rank: Super Contributor
timestamp: May 18, 2023, 03:57:53 pm
content: I was working on a prototype for Xilinx JTAG programmer based on FT2232H and decided to give a go to via-in-a-pad process because I plan to use it later for a much more complex design. Attached are a couple of photos, QFN pad has 25 0.2 mm vias arranged as a 5x5 grid, and there are some vias around U1. This is a 4 layer board, so I had to pay a bit extra for the via-in-a-pad process, but I can say that I'm very positively impressed with results I see!

author: mtwieg
author_rank: Frequent Contributor
timestamp: May 22, 2023, 12:01:36 pm
content: I've wondered about doing VIP with JLPCB but never tried it. What specifically did you select when placing the order? What's the drill size for the vias? Did you specify filled and overplated vias?At a glance it looks like they did fill+plate on all vias. But I think I can barely make out the 5x5 array of dimples on the QFN... either way it looks totally solderable.

author: asmi
author_rank: Super Contributor
timestamp: May 22, 2023, 04:48:54 pm
content: Quote from: mtwieg on May 22, 2023, 12:01:36 pmSee screenshot in attachment for order details.Quote from: mtwieg on May 22, 2023, 12:01:36 pmYep, I've already assembled the board, and had no problems with soldering whatsoever. And no solder bleeding through vias, which is why I made them 0.2 mm to begin with. Now that I'm more confident with the process, I can respec those vias to be 0.3 mm and save some money (my order would be about $30 cheaper) in case I don't need such small vias elsewhere (like in BGA).

author: tszaboo
author_rank: Super Contributor
timestamp: May 22, 2023, 07:48:16 pm
content: You don't need to pay for via-in-pad for those vias. Via in pad is good if you want to have them in 0402 components, or the small pads of QFN. For the thermal pad of a QFN, just place 0.3mm regular vias, it will solder just fine. What I mean is that this is completely normal production practice, that you will get on normal boards without paying extra, and your assembly house will make those boards with 99.9+% yield.

author: asmi
author_rank: Super Contributor
timestamp: May 22, 2023, 09:20:53 pm
content: Quote from: tszaboo on May 22, 2023, 07:48:16 pmI can decide by myself what I need and what I don't. In case you haven't read the first post - this is a test to see how process works so that I can use it in other designs which DO need it. Besides, this option only costs $18, so I can see many people opting for that just for aesthetics alone - it looks MUCH better in my opinion even if it's not required from strictly technological reasons.

author: mtwieg
author_rank: Frequent Contributor
timestamp: May 23, 2023, 10:01:26 pm
content: Quote from: tszaboo on May 22, 2023, 07:48:16 pmWhile you can get functioning results with un-filled VIP, I wonder what you'd see if you looked at the thermal pad under x ray. You'll likely see some large solder voids, which isn't acceptable for certain industries/applications.

author: tszaboo
author_rank: Super Contributor
timestamp: May 24, 2023, 10:48:12 am
content: Quote from: mtwieg on May 23, 2023, 10:01:26 pmThere are test reports available for this:https://www.ti.com/lit/an/slua271b/slua271b.pdfI've seen other reports that were saying that you can have as much as 70% voids without significant performance loss.Quote from: asmi on May 22, 2023, 09:20:53 pmThere is really no reason to be so defensive about this.