Riveting pcb holes - engineering type input sought!

**HankMcSpank** · 15-04-2015

Long time no post how you all doin'?!!! :-)

I need your input!!

I've a little widget that I used to make ...basically a pcb with 2 x m3 holes tapped into it ....it's looking like that I'm going to have to dust it down & start selling again (sigh).

Problem: Tapping M3 holes directly into 1.6mm thick pcb is not strong enough (especially since I use paper based FR2 board vs. fibre glass based FR4...this is because FR2 is a whole lot cheaper & presents a far nicer grade of dust for inhaling when I mill it!) .....at the moment I tap the m3 holes, & put nuts onto the screw behind to reinforce the hole - not ideal). So I need a more robust way of reinforcing the holes in the pcb.

These self broaching nuts initially seemed a good option....http://www.rapidonline.com/mechanica...-of-50-33-3802 .. except the hole has to be 4.2mm to receive those nuts ....and they have to be a couple of millimetres away from the board edge (not sure I understand their "Min. radius thickness from sheet edge" ...is that to the edge of the nut or the centre of the nut?) ...this last bit is the deal breaker (I can't move the holes, and with a 4.2mm hole to receive those nut, it'd be too close to the edge of the pcb...it'll probably crack when inserting the nut under pressure).

ok, second option, re-inforce the hole with a rivet, so I was looking at these copper rivets...

http://www.aliexpress.com/store/prod...271034053.html

their hole is 2.5mm diameter ...bearing in mind I need an M3 tap, that seems in the ballpark, but I then worry how much of the rivet would even left after the M3 thread was tapped inside it??

My main problem though is how do you even crimp something like that? (it'd need a die /punch of some kind or other, but I can't even begin to work out where I'd source one from?!!)

Cheers in advance!

**Jonathan** · 15-04-2015

Slightly off off topic, but have you considered getting the PCB manufactured? It's pretty cheap in China.

You can get riveting tools to use as a method for making vias in PCBs, but they're too small. Maybe something to imitate.

Instead of riveting, perhaps you could use a lathe to machine your own insert from brass and solder it to the board on both sides, or would that not be strong enough?

**HankMcSpank** · 15-04-2015

Hi Jonathan...thanks (as ever) for the input.

Truth be told, I don't trust Chinese fab houses.

This is fairly low run....I'm probably talking 40pcs maximum per annum .....it only takes me about 15 minutes to mill 10 nested copies of my pcb layout, therefore just over an hour to mill one years supply of the pcbs needed!

Actually, I think I've found the tool I need....

http://www.mouser.com/ProductDetail/...8SqT5kVQ%3D%3D

which crimps these eyelets.....

http://www.mouser.com/Search/Product...tP4fbZOg%3d%3d (1/8" ....they'd probably do for M3)

The rivet press for riveting thru hole rivets for PCBs costs about £500!

Re using a lathe...I don't have one, & that sounds time intensive (& I'm trying to get the time down to build one of my widgets....it already takes me about 1.5hrs (I'd rather use something already available & cheap as chips...hence looking at brass/copper rivets/eyelets) ....also I suck with a lathe

(Incidentally, I've found a cheapskates method for PCB stencils....from drinks cans! https://www.youtube.com/watch?v=JWUJtmgh55M .....except he's etching, that could readily be milled)

**cropwell** · 16-04-2015

I read your requirements about position of the hole and I thought maybe a steel M3 riv-nut could be soldered into the PCB. The one I have are 4.7mm OD and 8.7mm long. I have the mandrel for the setting tool, but they are fragile and hard to come by, but it sounds as though setting them in the PCB would not be an option anyway.

**mekanik** · 16-04-2015

Looks like the best option is going to be soldering to the board, i would get some 2 or 3mm brass plate cut off a strip drill and tap several holes and the cut it to a length that dives you a reasonable surface area, then solder it to the board.
You could do the drilling on your cnc and knock off a bath in a reasonable amount of time.
Regards
Mike

**Boyan Silyavski** · 17-04-2015

Any leather eyelet pliers will do the job and if they don't reach, then refabricate something similar with longer reach from them . If it was me i would simply instant glue each side a washer. If the glue is good it would stick forever.

Plus, nobody could convince me that the PCB eyelet which they sell for 10cents is not in fact leather eyelet.

**i2i** · 18-04-2015

Originally Posted by HankMcSpank

Long time no post how you all doin'?!!! :-)

I need your input!!

I've a little widget that I used to make ...basically a pcb with 2 x m3 holes tapped into it ....it's looking like that I'm going to have to dust it down & start selling again (sigh).

Problem: Tapping M3 holes directly into 1.6mm thick pcb is not strong enough (especially since I use paper based FR2 board vs. fibre glass based FR4...this is because FR2 is a whole lot cheaper & presents a far nicer grade of dust for inhaling when I mill it!) .....at the moment I tap the m3 holes, & put nuts onto the screw behind to reinforce the hole - not ideal). So I need a more robust way of reinforcing the holes in the pcb.

These self broaching nuts initially seemed a good option....http://www.rapidonline.com/mechanica...-of-50-33-3802 .. except the hole has to be 4.2mm to receive those nuts ....and they have to be a couple of millimetres away from the board edge (not sure I understand their "Min. radius thickness from sheet edge" ...is that to the edge of the nut or the centre of the nut?) ...this last bit is the deal breaker (I can't move the holes, and with a 4.2mm hole to receive those nut, it'd be too close to the edge of the pcb...it'll probably crack when inserting the nut under pressure).

ok, second option, re-inforce the hole with a rivet, so I was looking at these copper rivets...

http://www.aliexpress.com/store/prod...271034053.html

their hole is 2.5mm diameter ...bearing in mind I need an M3 tap, that seems in the ballpark, but I then worry how much of the rivet would even left after the M3 thread was tapped inside it??

My main problem though is how do you even crimp something like that? (it'd need a die /punch of some kind or other, but I can't even begin to work out where I'd source one from?!!)

Cheers in advance!

How about soldering 3mm brass nuts to the top or bottom of the board.

**HankMcSpank** · 18-04-2015

Thanks guys....great input. I can't solder brass nuts, because it a single sided board ....and the solder side is on the wrong side for the nut to go on :-(

silyavski ...I'd forgot that I've actually got one of those tools lying around somehwre (probably in my loft), I'll dig it out & give it a go!

**mekanik** · 19-04-2015

Although the link to the intended rivets gives a reference (h) for the wall thickness the seller does not specify a size. Thread depth for 3mm thread is 0.3mm so it is going to have to be about 0.5mm wall thickness to give you a bit of lee way.
Can to send a quick sketch on how you need to use the holes for fixing and why you cant solder a nut/plate to the board.
Regards
Mike

**HankMcSpank** · 20-04-2015

Originally Posted by mekanik

Can to send a quick sketch on how you need to use the holes for fixing and why you cant solder a nut/plate to the board.

For now, I'd rather not post my drawings, but I can't solder a nut becuase like I say it's single sided pcb ....and on the copper side of the pcb, the enclosure will be butting up against the pcb surface.....if I soldered a nut on that particular side, then there's be a gap equal to the height of the nut that was soldered onto the pcb (which would look awful)