[sdiy] Front panel and PCB design tactics

[rsdio at audiobanshee.com]

Thanks, Tom.

I almost always select SMD components that have a PCB fixing post. This doesn't prevent the part from being lifted directly away (perpendicular) from the PCB, but it does provide relief against pressure in other directions. The 3.5 mm jack that I found from Switchcraft is horizontally mounted, and has two fixing posts, meaning that inserting a jack would be pressing against these posts instead of just relying upon the SMD pads. Of course, I was hoping to find something with threaded sleeves to further take the plug insertion stress off the pads.

I do see your point that any torque on the PCB will be stressing the pads, even with the posts taking some of that. I was assuming that folks would have their modular all secured, but I suppose frequent changes might put stress on the PCB of nearby modules, so a weak link is not ideal.

Brian


On Apr 26, 2015, at 12:06 AM, Tom Farrand <mbedtom at gmail.com> wrote:
> It has been my experience that surface-mount components which provide mechanical mounting, is not optimal.  One must rely on track-to-substrate bonding for mechanical integrity.  Too many times I have experienced connectors and such which break loose from the substrate and create annoying repair headaches.  After tacking down the errant part and replacing the inevitable lifted track, I must epoxy the part's body to reinstate mechanical "grip".  I far prefer through-hole parts for that reason.  Yes, selective soldering is another cost adder in the manufacturing process but is much more robust.  With through-hole, the solder will wick up the leg and provide a mechanical bond on both the top and bottom of the substrate (assuming plated-through holes).  Over time, a reduced fallout rate is cheaper insurance than returned units that will probably be scrapped.
> 
> For a similar reason I am not a fan of surface-mount electrolytic capacitors which are "tall".  Tall caps will be whacked now and then and when they are, there goes the track!  If you must have tall, surface-mount electrolytics, put a couple vias-in-pads for the electrolytics and widen the footprint tracks for a bit more solder.  (Don't forget to swell the paste mask a bit such that additional solder is available for a bit more surface area of the component footprint.)  The vias will wick upward (downward, in this case) as described previously and help hold things together.  Nowadays, tolerances are tight enough that via-in-pad should be fine.  Lastly, you can have the vias filled, but as you might guess, that is also a cost adder but makes for a better mechanical connection.