Dealing with mechanical stress on PCBs ?!  - Page 1
Forum section: electronics / projects

author: suku
author_rank: Contributor
timestamp: September 28, 2016, 04:59:21 pm
content: On my PCB I have all the UI stuff mounted directly on the board (tactile switches and potentiometers). It worked fine for a while but after 6 months of abuse some of the controls started to fail due to the flexing on the board... The final enclosure will significantly reduce the mechanical stress on the board, but I'd still want to make the PCB more durable...Any ideas what would help the most? I can't really increase the overall PCB thickness but I could...- specify thicker copper layer (currently 1oz)- use thicker trace width (currently using 16mil)- maybe larger pads for through-hole switches?Thanks for the help!

author: Jeroen3
author_rank: Super Contributor
timestamp: September 28, 2016, 05:56:22 pm
content: Add extra supports from the enclosure.Use potting compound to make it a brick.

author: Ice-Tea
author_rank: Super Contributor
timestamp: September 28, 2016, 06:26:40 pm
content: Stiffener bussbars.

author: Kleinstein
author_rank: Super Contributor
timestamp: September 28, 2016, 08:08:28 pm
content: Larger pads might help a little. Thicker copper or wider lines don't help much.Having the mounting points at the right place and maybe having a few more might also help.

author: m98
author_rank: Frequent Contributor
timestamp: September 28, 2016, 08:58:26 pm
content: Add more mounting points evenly distributed in the high-stress areas of the board and back supports for the board to the enclosure. Larger pads could help, but only if the current ones are undersized. Might also consider a more ductile solder alloy like for example Sn95Ag5, which has similar to better properties than the more common leaded solder alloys.

author: calexanian
author_rank: Super Contributor
timestamp: September 28, 2016, 11:41:50 pm
content: +1 for more mounting points in strategic locations. Also a small piece of aluminum extruded U channel can do wonders if mounting points would. It be practical. Anything that adds a perpindicular rigid plane will help in that scenario. You could go with thicker boards, but it's not really the best option.

author: wraper
author_rank: Unknown
timestamp: September 28, 2016, 11:50:35 pm
content: If it does not have ground plane filling, then use it. Makes PCB significantly stuffier.

author: technotronix
author_rank: Regular Contributor
timestamp: September 29, 2016, 07:26:35 am
content: See the way to deal with a mechanical stress on PCBs.http://electronicdesign.com/boards/pcb-design-and-its-impact-device-reliability

author: KL27x
author_rank: Super Contributor
timestamp: September 29, 2016, 09:05:51 am
content: Tighter holes?

author: Niklas
author_rank: Frequent Contributor
timestamp: September 29, 2016, 10:14:36 am
content: As one soldering expert at Fraunhofer Institute said during a discussion: Everything breaks, it is just a matter of how many cycles.The key thing is to remove the mechanical stress from the solder joints and the points you listed are not going to help you very much in solving the mechanical strength.Some sources of mechanical stress:- Pushing and bending on buttons, knobs, connectors. SMD USB mini connectors where very sensitive...- Vibration and dropping on the floor- Thermal expansion/contraction- Ageing, plastic materials releases softeners and other chemicals. Annealing. Even 1% can make a huge difference if the distance is long enough.At first it might sound like a good idea to fix every single connector and pushbutton soldered on the PCBA to the housing. But you must also consider the operating conditions, for instance operating temperature range, and the materials that are used in the enclosure. Plastic materials might have a much larger thermal expansion than the PCB laminate. Sometimes it is better to have on fixed point, like all connectors along one edge, and let all the other thing be floating with a flexible connection.I have seen some pushbutton extenders that had mechanical stops that touched the PCB surface to offload the tactile switch. Looked like a table where the bottom surface interfaced the switch and the 4 legs limited the movement.