ring terminal to PCB connection

[makni]

Hello,

I have a BLDC motor control PCB (custom board - 15A peak). The requirements for that board is to have low profile (max around 15mm-20mm)
The chosen BLDC come with ring terminal crimp that need to be connected to "Mac8 M2 Screw Through Hole Tap" using a screw. (please google the name and you'll get the full picture of the setup)
We faced sometimes a loose screws due to vibration of the motor.

The purpose of this post is to check other possible method to connect the ring terminal crimp to the PCB based on all the listed requirements.
If you don't have any potential idea i was thinking about using silicone, glue or solder to strengthen the connection and remove the vibration issues but i would like to have more idea about what kind of silicone i need to use or in case of repair, how i can dissolve it to access to the terminals?

Thank you.

[ebastler]

The tap ring is soldered into the PCB, right? And I understand that it is not the ring/PCB connection which comes loose, but the screw in the tap?

Wouldn't the standard approach be to use a toothed locking washer, and/or thread locking liquid like Loctite 270 or 243 (applied onto the thread before inserting the screw)?

[makni]

Hello,

Yes I was actually thinking about the locking washer, but regarding the thread locking liquid, as i am not familiar with it. Is it permanent or can be removed in case of repair?

Thank you for your suggestions.

[ebastler]

There are different types of thread locking liquids. Loctite 243 is a well-known "non-permanent" type: The screw can still be loosened with hand tools. Loctite 270 and 271 are high-strength types -- much more difficult to loosen again, and typically used when there is no need to open the connection later (e.g. for service).

https://next.henkel-adhesives.com/us/en/articles/choosing-the-right-threadlocker.html

[jpanhalt]

If those are posts are to be swagged to the PCB and the terminal screwed to them, the PCB would be a weak point.  If possible, I would use a screw and nut* with Loctite or similar as suggested.  The reason is that the screw and nut do not depend on the PCB to keep them from turning if they need to be removed.

*The nut can be soldered to the PCB, so it is less likely to turn as in the attached.

[squadchannel]

Why not screw/nut directly to the board?

[ebastler]

In my understanding, the PCB with the "tap" mounts already exists -- at least the design, probably also manufactured units. At this time the OP seems to be looking for process improvements they can use to attach the motor leads securely to these taps.

[squadchannel]

no choice, will have to use Loctite.

my concern is attaching wiring that can flow 15A to the SMD post. will probably strip the traces.
i believe that these SMD posts are for mounting daughter boards.
says the screw size is M2, maybe an RC motor driver board.

[jpanhalt]

My reason for suggesting a fixed nut rather than a nut and screw is that the latter is more complicated to do, particularly with small fasteners.  A swagged nut to the board would be simple, but all of the swagged nuts I saw were round, not hex.  With thread locking, the force needed to remove the screw may simply make a nut swagged to a PCB turn, particularly if a "non-removable" threadlocker is used. (There's another thread here about removing rivets from a PCB where the same problem exists.)  Of course, none of that matters if the boards have already been designed and produced.  A star washer and removable threadlocker might be the best option.

[tszaboo]

If you don't want to change everything, I have a suggestion for you. This could work better than Loctite, as that could go between the contacts if applied incorrectly.
You have a terminal with hole, and a standard bolt. Change it to a terminal with external thread and a DIN985 locknut. Those will stay there no matter the vibration. And use torque controlled drivers in production.

[ajb]

A threadlocking compound like ebastler suggests is a good idea.  Silicone isn't as helpful because of how flexible it is, it may still allow the connection to move.  It might keep a wire from coming loose and flapping around, though. 

In terms of lock washers, 'conical spring' or 'belleville' lock washers are generally the best.  'Wedge lock' washers are even better, but very expensive and more suited to larger fasteners.  Toothed or 'star' lock washers can be okay if the teeth are able to bite into the base material properly.  The lock washers that look like a single coil of a spring are terrible and may be worse than no lock washer at all in some cases.

Controlling torque in production is also important as tszaboo says, with such small fasteners there is a very narrow range between enough torque to hold and enough torque to break the head off of the screw.