BGA package right on edge of the PCB - Page 1
Forum section: electronics / projects

author: TheUnnamedNewbie
author_rank: Super Contributor
timestamp: August 30, 2022, 07:48:09 am
content: So for a hypothetical project, that involves making a hypothetical BGA, it would be interesting if we could 'force' users to put the BGA right on the edge of the PCB, such that the edge of the BGA lines up with an edge of the PCB. It doesn't necesarally have to be the outer edge, a hole would also be fine.Is there any reason that this is not viable? Yes, it will make fan-out harder (and force the end users to use things like via-in-pad), but that would be an acceptable tradeoff.

author: oz2cpu
author_rank: Frequent Contributor
timestamp: August 30, 2022, 08:22:43 am
content: i design pcb's with BGA and stuff like this for a living, the closest i have ever done a design,is halve the bga package size, as the distance to pcb edge, and it was not my free choose,I would not recommend this, for many obvious reasons.your post lack reasons for you bad and wrong choice.

author: TheUnnamedNewbie
author_rank: Super Contributor
timestamp: August 30, 2022, 09:23:35 am
content: I cannot disclose the reasons for this 'bad and wrong' choice of placement due to various company/legal reasons. You could of course attempt to expand on the 'obvious' reasons, besides stating they are obvious, so I can figure out if they are in fact significant issues we cannot overcome.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: August 30, 2022, 12:21:33 pm
content: As a hint given OP's background, I would guess it has to do with on-chip mmwave communications or something like that. So, think keep-out region of RF modules, but chip scale.Or that might be completely off base, who knows.For my part, I don't think there's anything wrong with that? Maybe stress raiser, annoying to fan out of course, just use enough layers, and VIP if needed.Tim

author: Ice-Tea
author_rank: Super Contributor
timestamp: August 30, 2022, 12:46:17 pm
content: How would you panelize the PCB's? How would you de-panelize the PCBs?One reason for keeping distance to the board-edge is a V-cut, the associated blade moving along the edge and the mechanical stress that goes with it. Another is the need to actually clamp the board when it moves through P&P + soldering.

author: mikerj
author_rank: Super Contributor
timestamp: August 30, 2022, 01:09:48 pm
content: Stress on the solder joints is the usual reason this would be avoided, and if the BGA part is a chipscale/wafer level packaged device then placement near the edge of the PCB also invites physical damage

author: TheUnnamedNewbie
author_rank: Super Contributor
timestamp: August 30, 2022, 02:09:41 pm
content: Quote from: T3sl4co1l on August 30, 2022, 12:21:33 pmI guess I can neither confirm nor deny thatQuote from: Ice-Tea on August 30, 2022, 12:46:17 pmThis would be on quite small PCBs (I think <10cm x 10cm or even less), so I imagine assembly happens while the PCBs are still a panel (thus they wouldn't be on the edge of the panel, still space for clamping).I've seen the stress-on-solder-balls come up a lot, which is a good point that I didn't think about. I wonder if I can mitigate this by specifying a milled section (so there is no v-groove nearby) right at the BGA edge, so that none of the stresses that would be translated through a V-groove can make it to the chip.After all, when you consider things like smartphones, smartwatches, etc, they will also not leave a huge gap of a few millimeters next to the edges right?

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: August 30, 2022, 02:16:52 pm
content: Quote from: mikerj on August 30, 2022, 01:09:48 pmThat would easily be solved using a slot alongside the part

author: coromonadalix
author_rank: Super Contributor
timestamp: August 30, 2022, 02:34:39 pm
content: Not viable for mechanical and other reasons, put it away from the edges, we had many problemsWe use big fpga in bga format, in HF / UHF frequencies stuff, we had to center it on the pcb and displace everything around it, heat sink wise, thermal dissipation wise, mecanical stress etc ....I think you can understand

author: TheUnnamedNewbie
author_rank: Super Contributor
timestamp: August 30, 2022, 02:40:05 pm
content: Perhaps a detail I can add: We are not talking about a big BGA here. This is a BGA that measure <10x10 mm, and doesn't require heatsinking or anything.

author: Miyuki
author_rank: Frequent Contributor
timestamp: August 30, 2022, 04:17:19 pm
content: Do you mean something like this?It is nicely packed right to the edgesBut they are big packages with relative few data pads, as most memory chips are relative bigAnd even the processor, in this case, has pinout optimized to be in this location

author: langwadt
author_rank: Super Contributor
timestamp: August 30, 2022, 04:29:59 pm
content: Quote from: Miyuki on August 30, 2022, 04:17:19 pmthis on might as well be on the edge,https://www.digikey.ee/-/media/Images/Product%20Highlights/T/Trenz/TE0722%20Zynq%20DIPFORTy1%20Soft%20Propeller%20Module/trenz-electronic-te0722-large.jpg