High density PCB - Page 1
Forum section: electronics / projects

author: hamdi.tn
author_rank: Frequent Contributor
timestamp: September 16, 2015, 09:17:44 am
content: Hi everyone, am designing a board with almost 100 component in 35mm x 35mm pcb, usable surface is nearly the 1/4 of that. So components are too close and am worried about the manufacturability of the board, not the pcb istelf but how easy placement will be. what IPC standard define the minimum clearance between different type of part and package ?Thanks

author: daqq
author_rank: Super Contributor
timestamp: September 16, 2015, 10:26:13 am
content: You'd best consult this with your assembly house if they have such a capability.

author: matseng
author_rank: Frequent Contributor
timestamp: September 16, 2015, 11:01:32 am
content: What is the cause of the (possible) problem with densely populated boards?I guess it's not the pick n place itself since the parts are put down onto the board straight down. Is it the solder paste stencils that gets too flimsy by all the holes being too close?

author: hamdi.tn
author_rank: Frequent Contributor
timestamp: September 16, 2015, 11:10:51 am
content: i don't think solder past is a problem , some part pad are too close to each other more than they can be close to any other part pad.am more worried about the pick & place, i have no much knowledge what possible problem are but i guess high density board are challenging during assembly, so if anyone with manufacturing knowledge can share his experience. what can go wrong with this kind of board and related to the design itself is exactly the kind of information am looking for

author: T3sl4co1l
author_rank: Super Contributor
timestamp: September 16, 2015, 01:39:19 pm
content: IPC recommended minimum is something like 0.5-1.0mm, on a grid. I've seen DFM reports flagging 30 to 150 mils (0.8-3.75mm) depending on component type, which I'm sure will be different for other manufacturers. I think the reason for those were mostly rework -- specifically the 150 mil was for QFN, DFN, LGA, etc. types. Not so much due to mechanical limitations of the placers.So if you want to try for tighter than that, like daqq said, probably best to check with the people who'd have to deal with it.Tim

author: marshallh
author_rank: Unknown
timestamp: September 16, 2015, 08:34:00 pm
content: Check with your assembler, for autoplaced smd parts it shouldn't matter, it will matter for distance between large connectors and small SMD parts, or anything that is hand placed.

author: hamdi.tn
author_rank: Frequent Contributor
timestamp: September 16, 2015, 09:22:59 pm
content: great So in theory their is no problem with autoplaced components it all depend on what my assembler is capable of. i will certainty check with my assembler.

author: ajb
author_rank: Super Contributor
timestamp: September 18, 2015, 07:10:53 pm
content: One particular thing to watch out for is big components that may have an effect on the heat flow through the board during soldering. A tiny 0402 right next to a big power inductor, for instance, may be susceptible to tombstoning as the inductor will soak up a lot of heat during the soldering period, allowing the farther pad of the 0402 to reflow before the closer pad does. Something to discuss with your assembler if you have a mix of high and low thermal mass parts on the board.

author: hamdi.tn
author_rank: Frequent Contributor
timestamp: September 18, 2015, 08:16:05 pm
content: Quote from: ajb on September 18, 2015, 07:10:53 pmthe problem you mentioned is the very reason i started this thread, cause i do have 0402 next to all sort of stuff including 0402 next to inductor and next to smd usb connector. am still working on the board so i can have something to discuss with my assembler.