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1. 07:31 PM - Re: Re: OVM14 MkIII, rev P3 (Robert L. Nuckolls, III)
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| Subject: | Re: OVM14 MkIII, rev P3 |
At 09:29 PM 10/25/2023, you wrote:
>
>
>nuckolls.bob(at)aeroelect wrote:
> > Any assistance with making sure it wasn't a foggy day at this end
> is appreciated.
>
>It looks to me that the layout matches the schematic
>perfectly. Just a few comments to offer:
>Suggest not placing vias within the borders of SMD pads unless the they'll be
>filled with copper (at most board fabs, that's a high-cost option).
>As-is, the vias will tend to wick solder away from the components
>and may produce poor soldering results.
Good point. All our boards are hand-soldered. Vias
tend to be solder filled without compromising
smd attachment integrity.
> Are you planning to remove the middle leg of the SCR and
> surface-mount the part?
Yes.
>If so, there will be a trace and vias, connected to MT1, sitting
>directly under the
>MT2 tab. Unless the vias are tented, the one at the end of that trace will
>put exposed copper under the exposed tab, possibly touching.
Good catch! I've changed the LM431 to the alternate
SOT23 package with swapped cathode and reference pins.
That let me ground the anode without having to
'sneak' a trace between the SOT23 pins.
>It appears that the wires will be soldered to surface pads. I tried
>that once and it didn't take much effort for the wires pull pads
>off the board. Suggest using through-holes to attach wires -or- put
>drilled holes near the pads so that the wires can pass through
>the board from top to bottom for mechanical support before soldering.
We did that in earlier configurations of the
OVM but went to the 'tacking pad' for about
the last 20+ years of production. The flying
leads are held parallel to the ECB surface
under the heat-shrink enclosure. This puts
wire tension forces on the pad in shear which
proved adequate to task.
To facilitate proofing I temporarily widened
GND and BUS traces. They're now back to .015"
I'll do the fabrication paste-up tomorrow.
These boards fit into a 3 x 5 array on
ExpressPCB's standard 'proto' coupon. They'll
do 3 coupon a 3-day turn with solder-mask
for $90. That gets each board down to $2.
The bill of materials for the finished
device is looking really good!
I'll publish the BOM on the next revision
to the drawing package.
Thank you so much for your time and attention
to this project my friend!
Bob . . .
////
(o o)
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