Square Peg IN Round Hole

[dknguyen]

So apparently, a 20mil square peg won't fit into a 20 mil round hole. Go figure. Oh well, it's not like there weren't other mistakes on the PCB already. The more mistakes I find the better...so I can correct them and each mistake ends up being cheaper. How long do you keep your PCB design hanging around before you send it off? I had this one sitting around for 2 weeks, and a month after I sent it away I started to find all these mistakes- so of course when I called them they had already sent it off to be made.

[Cost Per Error] = [PCB Sunk Cost]/[# of Errors] = $100/7 = $14.28/error

 

[Sceadwian]

It's easy. Don't make mistakes. Go over the dimensional requirements of your components with a fine toothed comb. The square peg in the round hole is a good indication that you're not paying enough attention to clearances and geometry. This information is all readily available on the white sheets for your devices. There ?may be? some way of printing a 'proof' sheet of a PCB design using your PCB software on plain paper that includes dimensional refrences for the various holes and spacings. Even paying strict attention mistakes like that are going to happen.

 

[dknguyen]

The square peg in the round hole is a good indication that you're not paying enough attention to clearances and geometry.

I'm an EE! Not a CivE dammit! I am having trouble dealing with the positions of the mounting holes on my board though. The platform has some holes predrilled but I can't accurately measure them, and then in OrCAD, I I know of no way to type in placement coordinates for the parts so they are accurate relative to each other (at least when I placed them. Now that I think about it, I'm pretty sure I know how to do it). But still, it'd be nice to physically check it out somehow...

Other than fixing the msitakes, I've made a million improvements on the board anyways...so hopefully it will be worth it. I just hope this doesn't happen when I have to make boards that several hundred since they have some special requirements that can't be handled by BatchPCB's standard specs.

 

[kchriste]

So apparently, a 20mil square peg won't fit into a 20 mil round hole.

I'm sure a 1-ton press will dissagree with you.

But still, it'd be nice to physically check it out somehow...

You can't print it out, as suggested by Sceadwian, and stick the parts through the paper to check? This is what I've done with odd components in the past.

 

[dknguyen]

Never occured to me lol. My printer sits behind me so it never comes to mind.

 

[hjames]

Buy a cheap pair of calipers - I think plastic digital ones are in the US$40 range. They're pretty useful when you want to do a quick "paranoia check" on anything physical.

I think I've made layout mistakes on imperial/metric conversions, radius/diameter, drill size/plated size, left/right/up/down swaps, and having mounting holes offset by 100 mils due to PBKAC issues... Thankfully, I don't think I've made the same mistake twice, I just wander into new ones every now and then.

Also, be sure to have enough slack in the hole measurements so that you don't have to press-fit anything. If you want to be able to desolder the stuff, you want the hole to be as loose as reasonably possible...

 

[dknguyen]

Have you ever tried to desolder lead-free? It's an even bigger pain in the ass than soldering lead-free. I leave slack for the measurements, but it's hard to know just how much is enough. Usually I pick the upper limit and then round it up a bit more to a nice round number.

 

[hjames]

I haven't tried to desolder any thru-holes lately. I picked up the habit of notching the nozzle of the desolder pump so that the iron is still in contact with the pad when I trigger it - so I don't think the higher melting point/faster cooling will be too much of a problem. Then again I tend to have pretty lousy luck desoldering thru-hole parts in general. The only times when I am sure I can pull parts off is when there is enough space in the barrel so that I can do a "wiggle" check on each pins as I desolder them.

I tend to use PCB Express which has a bunch of fixed hole sizes. I usually round up to the next larger hole size (Above the one that would work). I think this usually pushes things at least 10-15 mils larger than what is required.