Spring washer on PCB 2

[Kennet B. Nielsen]

Hey everybody,
First entry - I am reviewing a design where the PCB is hold down by a screw and a spring disk.
Anyone using this particular design setup? Using a spring washer?

I have used the same approach on other designs but not clamping a PCB.

I have also heard that in some German design houses they don´t use spring washers anymore?!?!?

br KBN

 

[Tmoose]

Good morning,
The attached image did little to further my understanding of the design.
I'm guessing the gray disk (?) with a diagonal stripe on the OD, below the screw head (?) is the spring lock washer, and also am guessing the handsome green zone is the printed circuit board, and that the gray screw head is bearing directly on the washer that also in turn is bearing directly on the green stuff.

Several of the ISO standards for various "lock" washers have been "withdrawn", with no explanation.

https://en.wikipedia.org/wiki/List_of_DIN_standards#DIN_100_to_DIN_199

Mostly those with an initial overbite offset and sharp biting edges. DIN 127 for instance.
DIN 128 washers are configured differently, with the gap placed less like a cutting tool, on a continuously curved waved washer, but it also has been withdrawn.

The manufacturers of "other" style lock washers gleefully maintain that the styles were abandoned because did not work.
For structural joints I believe that is likely true (them not preventing fastener loosening.)
The survivors and replacements are mostly continuously curved or conical, with or without special surface textures.

If PCB means Printed Circuit Board then a sharp edged old school spring lock washer could tear it up pretty good if it rotates at all when the fastener is tightened.
>>Maybe<< a washer with some axial springiness could help maintain preload in a joint made with wimpy-*ss screws.
Without a bunch of testing that proved otherwise I would expect a steel flat washer would be necessary between the LW and the PCB to protect the PCB from being torn up, resulting in long term embedment and guaranteed fastener "loosening."

 

[Screwman1]

What is the purpose of the spring washer in the joint? We need to know that to understand what potential alternative solutions will work. Conical spring elements tend to have sharp outer edges that will cut into the board and traces and the wave washers have extremely low spring rates, helical washers simply are useless bits of flotsam in the world of fastening, etc. Lots of potential options but need to know design intent to proceed.

 

[TheTick]

Maybe a soft washer and a locknut (or screw with nylon lock element).