PCB Drilling

What form of laminate? resin paper or fiber glass? resin paper is normally punched and fiber glass 4 is normal.

Can someone tell me, remind me, what 14 mils is in metric units???

0.28 mm

11mil

actually, it's .35 mm.

14mils is .014 or 2.812mm. They teach this terminology in colleges. When you get into the real world of manufacturing you learn to call it fourteen thousandths.

Your decimal place has jumped. 2.812mm? 2.812mm = 0.1102 just up on 7/64. Mils thousands not hundredths.

Or if you're going to a machinist (s)he'll be saying "thou"

as in "I'll just take of a couple more thou for a clearance fit"

When you speak of "panels" of PCB's are you talking about fiberglass laminate

with 1 ounce (per square ft) copper? 1 ounce cu measures .0014" but the copper

usually isn't the greatest problem with drilling PCB's. It's the fiberglass substrate

that makes up the bulk of the thickness as well as drill wear. From that you would

need to calculate your feeds, speeds, chiploads and drill types. We would need

more info to help.

The stack up should not exceed the flute clearance of your drill. The peck in the drill cycle should not be much more than the diameter of the drill except maybe on the first peck. Are you doing this on a circuit board drilling machine or you doing it on a CNC milling machine, or manually? An air blast will help keep the chips clear of the drill and help reduce drill breakage. Glass reinforced epoxy is even more abrasive than glass reinforced phenolic and will greatly shorten drill life.

I don't know which school you all went to but 'mils' has nothing to do with the metric system.

1 mil = 0.001" = 1 thou = 0.0254mm (25.4 mm = 1")

10 mils = 0.01" = 10 thou = 0.254mm

Therfore, 14 mil = 0.014" = 14 thou = 0.3556mm

I hope this clears things up.

Dave Perry

Surrey Satellite Technology Ltd, UK

That was embarassing. I usually have to convert metric to english and so forgot to invert the .03937 decimal equivilant for 1mm. Or I could have just looked at the chart!

At least I am not alone.

If the original question referred to a #14 drill it would be .1820". If he meant 14(circular) mils, everyone would be wrong.

Blimey! what a lot of answers and different numbers!!

I only asked because I've only heard the Americans use the term 'mils', as a trainee I was always taught to say 'thou'...

Then metrication came along and mucked that up!

John.

What a confusion!!!!

Mils, Inch, Thou, mm

Dave Thanks(from all others) for clarification.

In a nutshell there is no perfect equivalents between metric and imperial.

Because of this I keep a "Decimal Equivalents" cheater card in my calculator case. It basically compares all the different drill sizes and where they fall in place against one another in terms of diameter. Looks something like:

0.3mm 0.0118"

0.32mm 0.0126"

80 0.0135"

0.35mm 0.0138"

79 0.0145"

0.38mm 0.0150"

1/64" 0.0156"

etc etc

As you can see the decimal equivalent in imperial is given for each drill size. This chart is quite precise, to a 10th of of a thou, but I have come across others that just had bad mistakes where I drilled a hole, expecting a large clearance fit just to find out someone had rounded and then someone else added extra zeros thinking the number was very precise.

As for PCBs...I've only really had success with a highspeed drill press (18,000rpm) and cheap steel bits that I bought at a hobby store. I'm sure for production this isn't the best but I could throw out 20 for the same price of just a couple, more brittle, carbide ones.

In the world (US) of PCB's, we use "mils" to address thousanths of an inch. There

is a metric to english conversion tool online that you can save and use. Look up

www.dadsrockshop.com.

Too bad we couldn't answer this guy's question.

But it was fun looking at the answers though...

I agree. I usually just absorb information and rarely put in my two cents, but

this was fun!