PCB Layout Suggestions - Page 1
Forum section: electronics / general

author: docmur
author_rank: Regular Contributor
timestamp: June 17, 2014, 10:54:10 pm
content: I'm almost finished my PCB layout and I was wondering if anyone has suggestions on improvements that I could make. I was also wondering if it would be okay to take the VIA's out from the exposed pads and just have them connect directly to the internal ground plane.J1 is a Mini USB Connector ( I HATE Micro ).U1 on the opposite layer from the USB is my battery charger circuit, it's charged off the USB, hence why I put it on the bottom layer.U2 is a Three-Axis, Digital MagnetometerP1 is a header to connect a battery to, might change to smaller pitchP2 is a Molex header which an LCD will plug into, the Molex header was listed in the LCD DatasheetU3 is the uC ( PIC24F64GB004 )U4 is a touch screen controllerAcross from the touchscreen is a footprint for a Bluetooth module.I still have to add a memory module and accelerator to the board, not exactly sure where to put them. The board is 6 layers, Top, Bottom, Internal VCC plane, Internal GND plane and two internal routing layers.The current dimensions are 24 x 30 mm, I can expand the board up to 37 x 30 mm.

author: Afrotechmods
author_rank: Unknown
timestamp: June 17, 2014, 11:04:32 pm
content: U3 is just a PIC. You'd only need that many vias if you needed to do a lot of heavy heatsinking of the IC. A single via would be fine and may give you a little more free space to route traces in the inner layers.

author: free_electron
author_rank: Super Contributor
timestamp: June 17, 2014, 11:11:38 pm
content: the groudn vis of the bluetooth module are touching pins on the flex connector ...and ,eh, not wanting to nitpick , but this is NOT a layout. it is barely a placement ...

author: zapta
author_rank: Super Contributor
timestamp: June 17, 2014, 11:35:43 pm
content: Having vias in the USB connector holding pads will make it less likely to peel off.If you want, I can point you to part number and footprint of micro USB connector that reflow very well.Sent from my Nexus 5 using Tapatalk

author: T3sl4co1l
author_rank: Super Contributor
timestamp: June 17, 2014, 11:43:33 pm
content: Mmm, I would argue that via-in-pad is worthwhile even for D/QFNs of low power: depending on your manufacturing process, the vias wick away solder so you don't have to use arbitrary solder paste shapes, and potentially, allow for leveling.But I'm not in manufacturing, so I don't know how often via-in-pad is actually troublesome. I just know what I've heard: yes it's okay, no it's horrible, yes tenting, no tenting, double tenting, plugging...The vias aren't going to hurt anything, assuming the footprint is okay otherwise (correct proportions of paste, pad dimensions; via diameter, count and board thickness; etc.). Might as well leave them there for when you do need a powerful chip..Tim

author: docmur
author_rank: Regular Contributor
timestamp: June 18, 2014, 01:04:02 am
content: I know the Bluetooth module is currently touching the molex connector, hence why I was wondering if it's safe to remove some of the VIA's. There really isn't a better place to put a Bluetooth module.

author: theatrus
author_rank: Frequent Contributor
timestamp: June 18, 2014, 04:50:49 am
content: Quote from: T3sl4co1l on June 17, 2014, 11:43:33 pmI've done via-in-pad for QFNs for exactly this reason. Hasn't bitten me yet for smaller production (~20k units).