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August 2018

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From:
"Stadem, Richard D" <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Stadem, Richard D
Date:
Mon, 20 Aug 2018 14:51:36 +0000
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A washer that is thicker on one half can be used to provide flat electrical connection to both halves of the step-up. This would be the only solution that will provide optimum electrical grounding.  Any ordinary flat washer that touches both halves of the hole is only going to provide electrical grounding at the very edge of the top board and at the edge of the washer on the lower surface, due to the washer being tilted.



-----Original Message-----

From: TechNet [mailto:[log in to unmask]] On Behalf Of Carl Van Wormer

Sent: Friday, August 17, 2018 4:52 PM

To: [log in to unmask]

Subject: Re: [TN] PWB PTH mounting Hole Damage



This looks like a job for a self-locking screw ( like this one: https://nylok.com/products/nylok-torq-strip), applied with a low torque setting (or just a very small diameter screwdriver that no user can use to over-tighten the screw).  This should allow a controlled pinch-mounting of the PC board assembly.  I agree with all commenters, this was not a good mechanical design.



Later,

Carl







Carl B. Van Wormer, P.E., AE7GD

Senior Hardware Engineer

Cipher Engineering LLC

    21195 NW Evergreen Pkwy Ste 209

    Hillsboro, OR  97124-7167

    503-617-7447x303

    [log in to unmask]     http://cipherengineering.com





-----Original Message-----

From: TechNet <[log in to unmask]> On Behalf Of [log in to unmask]

Sent: Friday, August 17, 2018 9:44 AM

To: [log in to unmask]

Subject: Re: [TN] PWB PTH mounting Hole Damage



Dell - Internal Use - Confidential  



Ioan,



The assembly came to me without a washer installed.   I just noticed the damage to the PTH copper surface when I removed the screw.   I have my two cents worth but waiting for forum input.

Now, if the assembly was tampered with before arriving at our lab I have no knowledge of that.   I will ask that question.



INHO the screw shank diameter to PWB PTH finish hole size is not accurate.



More pics will follow......



Givens:

>

> -          PWB PTH Slot Diameter, 138.450 mm

>

> -          Screw Head Diameter, 159.640 mm

>

> -          Screw Shank Diameter, 87.740 mm

>

> -          Potential mating overlap, 21.190 mm



   I am searching for guidelines for OVERLAP surface mating tolerance.



Victor,





-----Original Message-----

From: TechNet [mailto:[log in to unmask]] On Behalf Of Tempea, Ioan

Sent: Friday, August 17, 2018 11:15 AM

To: [log in to unmask]

Subject: Re: [TN] PWB PTH mounting Hole Damage



Victor,



Besides a washer, you also need to specify a torque. If the fastening operator happened to be the body building champion of the company, wanting to make sure the screw won't ever come out, this is what you end up with.



Cheers,



Ioan



-----Message d'origine-----

De : TechNet [mailto:[log in to unmask]] De la part de Robert Kondner Envoyé : August 17, 2018 11:39 AM À : [log in to unmask] Objet : Re: [TN] PWB PTH mounting Hole Damage



Hi,



 Holy Cow, No flat washerin the world is going to help here. When you tighten that screw the washer will tilt and only the very edge of the PCB "Hole" (I barely call it that) will provide support. If it is well tightened the washer will ben, PCB edges with crunch and the screw will bend. If you get it tight it will not stay tight as the PCB material is failing and it will crush causing the screw to become loose. 



You need something under the washer so the washer can come down flat. It might have seemed like a neat idea when it was designed but it does not look so hot now. 



Bob K.



-----Original Message-----

From: TechNet <[log in to unmask]> On Behalf Of Steve Gregory

Sent: Friday, August 17, 2018 11:17 AM

To: [log in to unmask]

Subject: Re: [TN] PWB PTH mounting Hole Damage



Hi Victor,



That's a pretty iffy looking mounting hole, and to tell you the truth, that kind of damage doesn't surprise me. There was a flat washer beneath that screw head wasn't there?



http://stevezeva.homestead.com/PTH_Diameter_vx_Screw_Head_Overlap.pptx



Steve



On Fri, Aug 17, 2018 at 8:54 AM, <[log in to unmask]> wrote:



> Fellow TechNetters:

>

>    I am searching for hardware mounting selection guidelines for the 

> purpose of avoiding future damage to PWB PTH external copper pad by 

> retaining screw head.

>

> Example pics and current dimensions have been sent to Steve Gregory, 

> [log in to unmask]<mailto:[log in to unmask]>

>

>

>

> Givens:

>

> -          PWB PTH Slot Diameter, 138.450 mm

>

> -          Screw Head Diameter, 159.640 mm

>

> -          Screw Shank Diameter, 87.740 mm

>

> -          Potential mating overlap, 21.190 mm

>

>

>

> Victor,

>







--

Steve Gregory

Kimco Design and Manufacturing

Process Engineer

(208) 322-0500 Ext. -3133



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