Re: Feedthough/via that straddles (i.e., is bisected by) the cut edge of a PCB?

On 5/30/2024 10:26 PM, Jasen Betts wrote:

On 2024-05-29, Don Y <blockedofcourse@foo.invalid> wrote:

On 5/29/2024 6:20 AM, dalai lamah wrote:

The keyword to look for is "castellated holes". The easier way to do it is
to find a manufacturer that explicitly supports them, and follow their
instructions. For example:
>
https://www.pcbway.com/pcb_prototype/What_are_Plated_Half_Holes_Castellated_Holes_.html

>
Excellent!  /Grazie tante/
>
A first pass through the description doesn't seem to EXPLICITLY say it but
it seems like they are implying that the drilling occurs ON the edge, and not
before milling?  I.e., each drilling action results in ONE such "hole" -- not
two HALF holes (on adjoining panelized boards)

 Usually the cutting is with a 2mm router and the holes are much
smaller than that.  so afterwards you only get one half of each hole.
 I suppose you could do vee groove instead of routing but I'd worry aboout the
copper tearing when the boards are separated. (or maybe the copper
would damage or contaminate the saw so they refuse this)
 as I unserstand it they are drilled at the same time as other plated
holes and slots  and then after plating, etching, and mask the edges are cut.
 

>
"...BEGINS with drilling ON the edge of the substrate..." (emphasis mine)

 I'm pretty sure they mean egde of your board outline.

 From the previously cited URL (reformatted for clarity):
    "The traditional process for manufacturing plated half-holes typically
    involves the following steps:
    - drilling
    - applying chemical copper to the panel
    - image transfer
    - pattern plating
    - film stripping
    - etching
    - solder mask layer printing
    - surface treatment
    - hole formation
    - contour milling.
    However, the above steps can result in decreased productivity and
    performance of the product."
I would assume milling the already plated hole being the problem.
    "Nowadays, the process of forming plated half-holes differs from
    the usual traditional methods.
    The process of forming plated half-holes begins with drilling
    /on the edge of the substrate/.
Suggesting that the drill actually is on the physical edge of the
material, not an edge that will be created after milling.
    "Therefore, it is crucial to use /specialized drilling equipment/
    as any deficiencies in the equipment can affect all subsequent steps.
Again, I would assume this is required because there will be a bending
moment applied to the drill bit as it encounters material only on one
"side" of the bit.  I.e., that it will want to bore a hole that is not
completely orthogonal to the board as it bends further from the intended
hole centerline as it proceeds further through the material.
    Once the preparation is completed, the next step is copper plating
    of the holes. Copper plating is equally essential as it ensures good
    conductivity for the components on the circuit board.
Note that they don't mention "specialized MILLING equipment" (to preserve
already plated holes with extra care)
?