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From: Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net>
Newsgroups: sci.electronics.design
Subject: Re: Feedthough/via that straddles (i.e., is bisected by) the
 cut edge of a PCB?
Date: Fri, 31 May 2024 12:45:21 -0000 (UTC)
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Don Y <blockedofcourse@foo.invalid> wrote:
> 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)
> 
> ?
> 
> 

That process wouldn’t leave copper hackles behind, so it obviously isn’t
universal. 

Cheers 

Phil Hobbs 

-- 
Dr Philip C D Hobbs  Principal Consultant  ElectroOptical Innovations LLC /
Hobbs ElectroOptics  Optics, Electro-optics, Photonics, Analog Electronics