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Solder dots around mounting hole - what are they for?

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eTobey:

--- 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, or is it just your idea of how it works? I really am surprised, that there is not much information about this aout there.

On my first picture, its easy visible, that the solder did not get squashed too far, and i cant see how this would affect the pcb at all. What i can think of is, that in the early days, the copper ring got detached from the PCB, so they put solder dots on it. And then there was multilayer and vias...

Nominal Animal:

--- 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.

wraper:

--- 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:

wraper:
Here is PCB from Phillips TV. Via stitching in between of solder dots but not underneath them. Also you don't want to deform material where holes are located. They can become nice fracture starting points. Arguing that holes in compression area will somehow make the material stronger is pure nonsense. Not to say do not forget FR-4 is not a homogenous material but a composite - epoxy impregnated glass fiber. By creating holes you interrupt glass fibers which bear the strength in material.


2N3055:
Just to confirm what was stated above, FR4 will plastically deform under pressure. An elastic washer or elastic material washer is recommended.

If you mount a heatsink through PCB, you are in world of trouble if you don't provide spring to keep constant pressure on heatsink. Heat makes creep even worse..

Solder dots are there to provide electrical contact.
Via stitching is sometimes provided to ensure good GND low impedance contact for inner layers to protective case..

I don't see copper adding much mechanical strength to glass fiber composite. It might help alleviate some creep on surface. But copper is quite soft...

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