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PTH on bendy power PCB is OK?

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cupoftea

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Hi,
Doing 4kW SMPS.
There are heavy transformers and inductors, (~0.5kG) on the main board....so its going to flex a bit.....so all other components on this board will be PTH only.....no SMD as it will crack and desolder. Would you think the PTH will be ok?
 

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Since you give us no information on how MUCH it will flex, I say, without reservation, that it will be fine. If it fails, don't blame me, because you didn't supply enough information for anyone to give you an intelligent answer.

Also, I'm pretty sure you can search for information on "allowable PCB deflection" or "allowable PCB flex".
Since you give us no information on how MUCH it will flex, I say, without reservation, that it will be fine. If it fails, don't blame me, because you didn't supply enough information for anyone to give you an intelligent answer.

Also, I'm pretty sure you can search for information on "allowable PCB deflection" or "allowable PCB flex".
 

Solution
Thanks, the cheap Chinese PCB places cant do >1.6mm cheap enough for our size of 4 layer board in our small QTY (<5)

So, if i may ask....We are doing a 2kW SMPS. PFC then Half Bridge LLC.

The main board has the chunky components on it and is rather large for this initial prototype (500mm x 400mm).

Therefore, we dare not put SMD on this potentially ‘bendy’ board. Though we need the Gate drive components to be SMD for sake of reducing stray L. As such, do you think the attached method is good for doing the gate drive with SMD daughter boards?

Its basically making the daughter board into a little kind of SMD component. (As SMD, The daughter board will be easier to remove if we need to, during testing.)

BTW, the cheap Chinese PCB Fabs don’t seem to be doing >1.6mm thickness on the cheap rates for our main board size, so we must use 1.6mm thick main board.

The below is the only thing I can find so far, but we need the legs to come “out” so we can solder them to the mains board SMD pads…..

https://uk.farnell.com/wurth-elektronik/61000418221/header-2-54mm-pin-smt-4way/dp/2356209

Is there such “SMD header” as in the attached picture? Basically we just want a header which will kind of put "legs" onto the daughter PCB.....to make it kind of like a SOIC8, type of thing...those kind of SMD "legs"

I mean, the below could kind of be hacked to do it..
https://uk.farnell.com/multicomp/mc34747/header-1-row-r-angle-3way/dp/1593427

....but its going to be a bit "raised" compared to a SOIC, kind of thing.
 

Attachments

  • Gate drive layout.jpg
    Gate drive layout.jpg
    63.6 KB · Views: 67
  • LLC gate drive.jpg
    LLC gate drive.jpg
    163.9 KB · Views: 71
Last edited:

Hi,
As we all know, if you have an SMPS on a big main board, which comprises heavy components, then you cant put SMD on it, as it will crack or go open when the main board flexes…so , for prototyping only, what about the attached method to get SMD on to a big main SMPS board?

Its just a little PCB, with SMD components on it…..and it has thru holes which line up with holes on the main PCB, and little bits of tinned copper wire are pushed through these holes to solder the little SMD PCB to the main board.
....there aren't even any "sticking out legs", so lead inductances will be to a minimum, which is good for things like gate drive componentry and current sense circuitry etc.

Do you see any problems with this?
 

Attachments

  • Little bit of PCB on main PCB.jpg
    Little bit of PCB on main PCB.jpg
    51.4 KB · Views: 65

So, We are doing 2Kw LLC Half bridge with vin = 400vdc.
The hi side drives are (on the prototype) being done as in the attached. The little sub-boards allow us to use SMD components without risk of them suffering possible flexion stress, which they would get if they were on the big main board.
Do you think this single SIL connection will stop flexion on the main board from occurring to the sub board?.....the header will be soldered into the main board

(also attached is an LTspice of this gate drive)
 

Attachments

  • Gate drive layout_hi side.jpg
    Gate drive layout_hi side.jpg
    420.9 KB · Views: 62
  • Gate drive cct_hi side.jpg
    Gate drive cct_hi side.jpg
    149.6 KB · Views: 62
  • LLC with chosen gate drive transformer.zip
    3.7 KB · Views: 83

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