General > General Technical Chat
Solder dots around mounting hole - what are they for?
Nominal Animal:
--- Quote from: wraper on October 22, 2023, 10:07:50 am ---
--- Quote from: Nominal Animal on October 22, 2023, 09:58:32 am ---
--- Quote from: eTobey on October 21, 2023, 05:05:17 pm ---
--- Quote from: Nominal Animal on October 21, 2023, 01:08:01 pm ---The reason it makes the PCB stronger is that it allows larger and more varied dynamic forces to elastically deform the PCB near the mounting hole without propagating the deformation further; keeping the deformation localized there.
--- End quote ---
Are there actually some theories or research about this
--- End quote ---
Sure. Talk to any mechanical engineer with related experience.
--- End quote ---
First you say a load of bull about vias underneath solder dots, then send to talk to mechanical engineer. Very informative argument :palm:
--- End quote ---
Bull? [Citation needed].
Also, why does your following post then support my argument? Can't you make up your mind about whether I'm talking bull, or are you confused as usual?
wraper:
--- Quote from: Nominal Animal on October 22, 2023, 01:36:08 pm ---
--- Quote from: wraper on October 22, 2023, 10:07:50 am ---
--- Quote from: Nominal Animal on October 22, 2023, 09:58:32 am ---
--- Quote from: eTobey on October 21, 2023, 05:05:17 pm ---
--- Quote from: Nominal Animal on October 21, 2023, 01:08:01 pm ---The reason it makes the PCB stronger is that it allows larger and more varied dynamic forces to elastically deform the PCB near the mounting hole without propagating the deformation further; keeping the deformation localized there.
--- End quote ---
Are there actually some theories or research about this
--- End quote ---
Sure. Talk to any mechanical engineer with related experience.
--- End quote ---
First you say a load of bull about vias underneath solder dots, then send to talk to mechanical engineer. Very informative argument :palm:
--- End quote ---
Bull? [Citation needed].
Also, why does your following post then support my argument? Can't you make up your mind about whether I'm talking bull, or are you confused as usual?
--- End quote ---
It supports none of what you said. There are no vias under solder dots, I scraped off one of them to show it. Via stitching is in places in between of the dots and do not get compressed by the screw. Looks the same as via stiching all along GND plane edges which helps preventing unintended antennas. As of citations, you so far provided exactly zero which would even slightly support your claims.
Nominal Animal:
Here is a more detailed reply, in case my previous one seems snarky. (It wasn't intended as such, as you'll see.)
--- Quote from: eTobey on October 21, 2023, 05:05:17 pm ---Are there actually some theories or research about this
--- End quote ---
This is governed by mechanical physics. The glass fiber-reinforced epoxy (especially FR4) is a viscoelastic substance, and its behaviour (especially under thermomechanical stress, i.e. expanding and shrinking when heated and cooled) is widely researched, but there do not seem to be any peer-reviewed published research as to what kind of mounting hole patterns yield the best results against damage due to mechanical forces.
(In particular, the way through holes are plated with copper seems to yield ductile copper in vias and PTHs; as opposed to the non-ductile copper foil in the conductive layers, as described in some of the articles you can find using Google Scholar.)
Thus, for a scientific explanation and references, you do need to go to a mechanical engineer with the experience and (simulation) tools in this area: a comparison model of a board with two through holes, one with vias, the other without, and a few runs of different forces acting on the holes (the same force for each hole, of course), simulated using finite element analysis software and existing FR4 models (especially the epoxy is tricky to get right), will show the exact situation.
(My claim: With vias, the stress is concentrated very close to the hole and the vias, and drops off much quicker as a function of distance from the mounting hole, compared to without.)
As to vias helping strenghten mounting holes, this came up here at EEVBlog forums a decade ago, when steaky1212 found that suggestion by Tom Hausherr (PCB Libraries author) on the Mentors website (Wayback Machine archived page). Quoting that blog:
--- Quote from: Tom Hausherr ---There are two primary reasons for adding vias to the supported mounting hole. The first was to insure that if the screw threads stripped the copper plating from the main hole that the vias would still provide adequate ground connections. The second reason was for additional support to prevent the PCB from crushing when too much torque was used to tighten the nut.
--- End quote ---
So no, it is not my idea. The explanation of how it works I wrote above is based on my understanding of the mechanics of the situation, trying to sketch out the mechanisms involved. I do now realize that effort was silly: I should simply have linked to that Wayback Machine blog article, because argumentum ab auctoritate is more acceptable to most members here than reasoning based on physics.
eTobey:
--- Quote from: Nominal Animal on October 22, 2023, 09:58:32 am ---Sure. Talk to any mechanical engineer with related experience.
--- End quote ---
That does not answer my question.
And any stress would IMHO just move around the hole. For your theory to work, it should be a groove around the hole. But that itself would cause to form a crack... And the mounting hole itself would be enough space for the material to go on compression.
Nominal Animal:
--- Quote from: eTobey on October 22, 2023, 04:20:34 pm ---For your theory to work, it should be a groove around the hole.
--- End quote ---
No, because the glass fiber-reinforced epoxy material (between the copper layers) is viscoelastic. It is obvious you're not going to trust anything I claim, so the suggestion to talk to a suitable engineer is sensible.
Navigation
[0] Message Index
[#] Next page
[*] Previous page
Go to full version