A specific PCB bad practise, term for it ?
N_Cook
big , thru-hole plated , but no eyelet/inserts used to fill the gap. So
1N4001 size leads in holes twice their diameter and 1N4148 in holes twice
their diameter. So not a case of only one drill size for all. So in area
terms about 1 to 4 ratio of lead to solder. Bad enough practise with proper
solder but with PbF, ring cracks starting all over.
Is it to avoid mutiny by the by-hand board populators ?
Smitty Two
wrote:
It's just careless design. As a contract assembly house, I see stuff
like that all the time. Surface mount footprints the wrong size for the
component, radial through holes for axial components, etc. ad infinitum.
Quoted a one-off prototype board last week at 3 hours, took 17, due to
documentation (and a slew of other) problems.
EEs should be allowed a pencil and a paper napkin to sketch out the
schematic, but after that, the board layout and overall product design
should be turned over to someone who's actually familiar with
manufacturing practices.
Jim Yanik
perhaps PCBs designed for machine parts insertion have those sort of
"oversize" thru-holes? Perhaps the insertion machine prefers big holes and
besides,they crimp over the leads anyways. Maybe it's too much trouble to
drill PCBs for different size thru-holes,and/or not worth the effort.
certainly stocking and inserting eyelets would be an additional,unnecessary
expense.
--
Jim Yanik
jyanik
at
localnet
dot com
Michael A. Terrell
We had a board house add 'thermal rings' to the mounting holes in a
500 MHz synthesizer. It played hell with the modules and sent the phase
noise through the roof but they said that they would no longer make them
the way we needed them. it also dropped the center frequency by about
100 MHz. I had to take some of the copper foil we used to seal the
shields on the modules and cover them, then solder them to the surface
and the plated through holes, till we could get the boards from another
supplier. They routinely made a couple dozen different boards for us,
prior to that. When they decided to change our layouts without
permission, we dropped them.
--
You can't fix stupid. You can't even put a Band-Aid™ on it, because it's
Teflon coated.
Michael A. Terrell
Jim Yanik wrote:
>
> "N_Cook" <div...@tcp.co.uk> wrote in news:iouqr0$pl0$1...@dont-email.me:
>
> > Where holes are drilled for thru-board components but of diameter far
> > too big , thru-hole plated , but no eyelet/inserts used to fill the
> > gap. So 1N4001 size leads in holes twice their diameter and 1N4148 in
> > holes twice their diameter. So not a case of only one drill size for
> > all. So in area terms about 1 to 4 ratio of lead to solder. Bad
> > enough practise with proper solder but with PbF, ring cracks starting
> > all over. Is it to avoid mutiny by the by-hand board populators ?
> >
> >
> >
>
> perhaps PCBs designed for machine parts insertion have those sort of
> "oversize" thru-holes? Perhaps the insertion machine prefers big holes and
> besides,they crimp over the leads anyways.
Microdyne stopped bending the leads or using the special cutters that
cripmed the leads back in the '80s to reduced damage to the PTH.
> Maybe it's too much trouble to
> drill PCBs for different size thru-holes,and/or not worth the effort.
It's more likely that there was no design review, or the cad operator
was too lazy to verify the hole sizes.
> certainly stocking and inserting eyelets would be an additional,unnecessary
> expense.
--
N_Cook
news:A8qdnSGUA-9Vfy7Q...@earthlink.com...
> Teflon coated.
As the drill bits tend to be very brittle carbide rather than HSS I imagine
doubling the drill bit diameter drops the breakage rate by 1/10 or so,
reduced bit replacement costs, plus reduced down-time manual intervention
to rectify stoppages, due to such breakages.
Michael A. Terrell
A properly run PCB drilling system doesn't break the bits, and they
are replaced before they are dull enough to cause a problem. If it is a
cheap, in house product, all bets are off. You can get properly made
boards, if buying the cheapest you can find is at the top of the list.
Boards with over sized holes use more chemicals to plate the PTH, and
waste solder in the hand or wave solder process. We stuffed and placed
our boards at Microdyne, but used outside PCB houses to produce the
blanks. Some of our boards were 16 layer and cost over $8,000 to
populate.
--
You can't fix stupid. You can't even put a Band-Aid™ on it, because it's
Teflon coated.
Jim Yanik
Tektronix still used the crimped over leads on their TH PCBs all the way up
to conversion to SMD boards,and that didn't happen until the late 1990's.
We didn't have much trouble with damaged thru-plated holes.
who where
wrote:
It was always my understanding that the "oversized" PTH was a
deliberate choice. If significant current needs to pass to both
planes, a (proper, of course, not RoHS) solder plug enhances the
through-plating's capability.
Michael A. Terrell
It makes more sense to just specify a thicker plating on the PTH.
Solder his a higher resistance, and is much weaker.
--
You can't fix stupid. You can't even put a Band-Aid™ on it, because it's
Teflon coated.
Smitty Two
who where <no...@home.net> wrote:
Um, I'm not an EE, but I thought the leg of the component helped to
carry current from one side of the board to the other.
who where
It does (doh!) but obviously the hole plating and the solder fill also
contribute to the overall conduction.
Sjouke Burry
The blob of solder has much less resistance than the
very thin copper surrounding the hole.
Mass counts here, and the copper is at a big disadvantage there.