Re: gEDA-user: an unplated via - a capacitor inside a board

[Gene Heskett <gene.heskett@xxxxxxxxxxx>]

On Sunday 12 March 2006 13:55, Karel Kulhavy wrote:
>On Sat, Mar 11, 2006 at 07:27:52PM -0300, Xtian Xultz wrote:
>> Em Sáb 11 Mar 2006 18:34, Karel Kulhavy escreveu:
>> > Let's say I have a ground plane on the solder side and power plane
>> > on the component side. I want to place a blocking capacitor
>> > between those two with the minimum parasitic inductance.
>> >
>> > The solution with minimum parasitic inductance is to make a via,
>> > but not plate it through, just leave the rings around the hole.
>> > Make the hole big enough for a 1206 capacitor to fit, insert a
>> > capacitor and solder on both sides.
>> >
>> > Is this possible with PCB?
>> >
>> > CL<
>>
>> I dont know if I understanded what you want, it is a little...
>> strange :D Well, I tryed with Xaw PCB (the latest version), didnt
>> create the output files, but I think it will work.
>> First, create a footprint with two pads, every pad must be big
>> enough to fit the hole where you will insert the capacitor, and have
>> sufficient solder area. Make one pad on the solder layer, and send
>> the other pad to the component layer. Give the first the padnumber
>> (n key) 1 and the other padnumer 2. Put one pad over the other. If
>> you like, create a silkscreen around him, select all, cut selection
>> to buffer, convert buffer to element. Put the part where you want.
>> Connect the pads to the polygons with thermals, or if you like,
>> connect them with a line, join the line with the polygon (j key) and
>> increase the size until he covers the entire pad.
>> Then, create a via with the hole size enough to insert the
>> capacitor, convert him to mounting hole (control+h) and place over
>> the part.
>
>Would it be possible to put this guide on the website (possibly
> stating that this is an innovative novel method that other programs
> are not having in their help)? ;-)
>
>I guess that there shouldn't be any problem with gas pressure inside
>because the hole is unplated and the gas can dissipate into/from the
>porous laminate.
>
Having tried to deal with this phenom over an extended period of time, 
I've found that in practice, its very very difficult when the 
outgassing is from the laminate itself, usually a paper-phenolic 
elcheapo product.  About the only way to get a decent joint seems to be 
by turning the iron down to just a few degrees above the solders 
eutectic temp, sitting it down in the puddle, applying a small amount 
of replacement flux as it gasses away, and simply wait patiently for 
the outgassing to stop enough that the joint is solid.  That can take 
up to 2-3 minutes!  This is very painfull for one who is accustomed to 
useing an iron warm enough to cut thru the oxide and let the solder 
flow quickly in order to prevent the dross formation that goes with the 
heat level from being a major factor in making a 'pretty' joint.

The most mixed company word I can use for that in my 57 years of running 
a soldering iron is PITA as it certifiably is one.

>
>> Thats it.
>> But, you must assure that your pcb fab does drilling process for
>> plated holes and for unplatted holes.
>> For example, my fab does not. In that case, I would insert a normal
>> via (but only after the complete routing is done, because to PCB its
>> a big short circuit). The hole will be metalized, but I rework the
>> boards redrilling the holes with a bit a little big.

Given sharp drills, thats the best way IMO.  You do not want a dull 
drill to smear the lining of the hole with a copper film.  And most of 
the substrates in use today are hell even on carbide drill bits.

-- 
Cheers, Gene
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