At 23.22 2012.06.19, you wrote:
>
>On Jun 18, 2012, at 11:18 PM, Electron wrote:
>
>> That means pretty "big" holes, so big that the component will fall=20
>down to the
>> floor if the board is turned to the other side=85
>
>I don't think I've ever assembled a professionally made PCB where the=20
>holes were small enough to hold in components just because of lead=20
>friction with the hole itself.  That would be a bit scary, given that=20
>you'll have drill tolerance plus copper plating tolerance plus=20
>tin/solder plating tolerance to modify the hole size from what you=20
>thought it would be.

Yup, I'll give up on this comfort and stick to 0.4mm diameter increase
of the hole vs the diagonal/diameter of the component pin. At least I'll
be now sure that barrel fill (if it's the right term) will be good. PTH
is really nice as it saves you from soldering both sides when you need
both to be connected (e.g. high current, or other reasons), and also
saves about 1mm of height, which in some cases may be useful.


>> Optimal pad size seems as a minimum twice the diameter of the hole,=20
> three times maximum (if board space allows).
>
>I like to think in terms of the "trace width" of the ring around the=20
>hole.  Obviously this shouldn't be any smaller than the minimum trace=20
>width supported by the manufacturer, and should generally be=20
>significantly larger to allow for easy soldering, and significantly=20
>larger again for mechanical strength if there are heavy components or=20
>external stress (connectors) involved.  Since a "typical" min trace=20
>width is 0.2mm, and a typical hole is 0.8mm, your "twice" allows for a=20
>ring width of 0.4mm, which is OK.  I usually fiddle with EAGLEs DRC=20
>parameters when I'm otherwise done, and make the rings as wide as I=20
>can without running into clearance issues.  OTOH, that's partially=20
>because I'm aiming at users with less soldering experience.

I learnt that rings should be as wide as possible anyway (within reason),
because even if you have a great soldering experience, you will probably
work faster, the joint will be more reliable, allow more current, etc..
of course within reason. ;) I usually make pads as small as possible
(within acceptable values) and then when the board is finished, I enlarge
all those that I can and makes sense to enlarge. But I don't want to
start with large pads because I tend to squeeze a lot of components per
square inch.


>EAGLE defaults to 25% of hole size for the ring (1.5x hole diameter=20
>for the pad), tempered by a minimum ring width=85

Interesting to know, thanks.

With kind regards,
Mario

>
>BillW
>
>
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