If no one finds a spec that
covers that, the rule of thumb is .010" over the lead diameter. You can go
down to .008", but it also has to do with the level of manufacturing and your
hole tolerance.
.005" is the bare minimum.
The old "common" tolerance used for the hole size was +/-.005", so if you
specify .010" over and the hole is at the minimum of the tolerance, you would
be left with .005" over.
In addition, there is the
mechanical tolerance. If you have, for example, a transformer with fixed
leads, it has about a +/-.010" tolerance in lead to lead spacing.
You either deal with that
during assembly or add that into the hole size. You can divide the between the
hole sizes. +.005" for one hole and +.005" for the other.
That would give you .015"
over the lead dia. Those leads usually have a large tolerance too and are
square. You wouldn't really want to add in all the tolerances, but a healthy
mix is necessary.
Probably none of this is
news to you, but is one reason that IPC can't really specify more than the
minimum clearance over the lead for solder flow. The rest is up to the
application.
I have a handy dandy
calculator for determining the pad sizes according to your requirements and
can calculate for square post too. www.pcbdr.com. the resource calculator can
also be used online of you have the Excel Plug in. (if you don't it won't
work. Simple)
Hi
everyone,
Does anyone know
of an IPC standard that will tell what a plated thru-hole size should be
depending on the diameter of the component that will be inserted. Example
would be a pin header, or a certain wire size. Basically, how much
bigger do you make the hole to accommodate the size needed so that you will
get a good solder joint, and designed well for
manufacturing.
Thanks,
Jim
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