Is It OK for Upside Down PCB/Circuit? - Page 1
Forum section: electronics / general

author: Mechatrommer
author_rank: Super Contributor
timestamp: August 27, 2011, 03:30:56 am
content: currently i'm placing parts on pcb software, and i'm running out of space from specification. so i think i have to split the parts, some on the bottom and some on above. parts on the above is directly interfacing to the user, pots and switches, and all of them are through hole. for the smd parts, i think i cannot split sides since to make reflow or such (diy and soldering) process later to become easier. so they all have to go to the bottom since i cannot put UI parts on the bottom. so most functionality (mcu, radio, amplifier) will be at the bottom, facing the plastic housing below, when assembled, we will see the large ground plane, with other UI parts on the top, hence "upside down pcb". my concern is, the circuit is detecting EMF pulse (with varying magnitude, max recorded around 30Vpp) from below, may it interfere with circuit functionality? will it corrupt/degrade mcu signal, radio signal and amplifier? if so, how do i overcome this? will just placing an aluminium foil in the housing (below) can avoid this emf interference? is this a common or bad practice? the space (housing) constraint is around 6 x 5 x 1.5 cm as pictured (with its pcb inside) below. hope to get some advice.

author: Kiriakos-GR
author_rank: Super Contributor
timestamp: August 27, 2011, 05:30:24 am
content: Shielding with out earth ground it works as antenna.I can not imagine if you are talking for a portable device or bench type?Even so to avoid interference you can use coaxial cables and feed thru capacitors.

author: Mechatrommer
author_rank: Super Contributor
timestamp: August 27, 2011, 07:11:33 pm
content: its not fun at all! err, its not you kiri my friend. i'm talking about routing that pcb. i have to further split the smd parts on both side, so now they mixed up i dont know how to reflow later. currently reading pcb tutorial rev a 29th june 2004, intro section. i have to agree with the author.Quoteand thats me even with this simple pcb.

author: Mechatrommer
author_rank: Super Contributor
timestamp: August 27, 2011, 07:15:59 pm
content: printing...

author: IanB
author_rank: Super Contributor
timestamp: August 27, 2011, 07:56:06 pm
content: Quote from: Mechatrommer on August 27, 2011, 07:11:33 pmI think you put all the small parts on the underside and reflow that, then you flip the board over and hand solder the bigger parts on the other side, then lastly you hand solder any through hole parts. So in your layout you would try to put the big SMT parts and the through hole parts on the opposite side from the smaller SMT parts.

author: Mechatrommer
author_rank: Super Contributor
timestamp: August 27, 2011, 10:40:35 pm
content: i think i have to solder the smd's on the bottom since the majority of smd and thruhole now on the top. and there's no big and small smd, they are all big smd. 0805 and soic only.

author: Frangible
author_rank: Regular Contributor
timestamp: August 28, 2011, 03:12:40 am
content: With proper bypassing and use of separate power and ground planes, you should be able to maintain isolation between the two sides, especially since it doesn't appear that you have any high voltage issues. Actually assembling the board seems to be the biggest challenge right now!

author: reagle
author_rank: Unknown
timestamp: September 03, 2011, 08:55:27 pm
content: We build boards with parts on both sides all the time at work. The key is to avoid heavy (not so much size but weight) components on the bottom, unless you can glue them in. Some people use special epoxy dispensing machines to glue parts and then they can be on any side. Otherwise stick to light parts on the bottom, run that through reflow, then place top side /heavy parts and reflow again. Usually the bottom does not melt enough to drop parts on a second reflow