Hmmm....I think Wayne know what he is doing and saying...
/Inge
The g-force experienced by an object is its acceleration relative to
free-fall.The term g-force is considered a misnomer, as g-force is not a
force but an acceleration.
----- Original Message -----
From: "Ahne Oosterhof" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Wednesday, December 16, 2009 6:36 PM
Subject: Re: [TN] Tensile strrength
> And I expected to see "force", not "acceleration".
> (The acceleration comes after the force has ripped the part off the
> board.)
>
>
> Having fun,
> Ahne
>
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of Thayer, Wayne - IIW
> Sent: Tuesday, 15 December, 2009 17:10
> To: [log in to unmask]
> Subject: Re: [TN] Tensile strrength
>
> Just to add a number to this, I get over 9000G's of acceleration on the
> parts near the ends of this board!
>
> Wayne Thayer
>
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of Inge
> Sent: Tuesday, December 15, 2009 12:47 PM
> To: [log in to unmask]
> Subject: Re: [TN] Tensile strrength
>
> Pradeep,
> you'll get into deep problems! Are you sure it's really 13,000 revolutions
> per MINUTE? And the board is not circular but rectangular. 13,000 rpm,
> that's the max for a Laverda racer bike. Imagine the littlest unbalance in
> such a machine, and there will be a catastroph. You have to consider:
> 1. The starting acceleration of that thing. If the start is too violent,
> you
> can get an acceleration force that will make the componensts fly off.
> 2. How do you make a perfect balance of a PWB? By counterweights or
> trimming
> by drilling holes etc ?
> 3. Even a very, very small wobbling will make the hole thing crash.
> 4. What kind of bearings? These may cause additional vibrations that can
> destroy sensitive components.
> 5. What kind of components are you going to use? Check if there are
> mechanical data available for each of them.
> 6. How do you dare give life expectancy (if this thing has to work for a
> long time.
> 7. There may be standing wave nodes between the mounting points. Not
> healthy
> for microvias and solder joints.
>
> Without knowing what strange design you are working with, I'd suggest a
> circular LTCC with all resistors and caps and maybe even inductors
> integrated in the ceramic. And make a symmetrical design. The balance must
> be as perfect as possible.
>
> Finally, when you test your product, see that you are not near it, because
> at that speed you have a dangerous thing in front of you. Your speed is
> not
> far from a spinning CD-ROM. Such a disk is very close to perfection in a
> balance point of view, nevertheless, things can happen. Some guys tested
> what happens with a CD, if you double the rotational speed, and you can
> see
> yourself below.
>
> http://www.qedata.se/e_js_n-cdrom.htm#inledning
>
> Good Luck and take care
>
> Inge
>
>
>
> ----- Original Message -----
> From: "Pradeep Menon" <[log in to unmask]>
> To: <[log in to unmask]>
> Sent: Tuesday, December 15, 2009 2:05 AM
> Subject: [TN] Tensile strrength
>
>
>> We have one of our customers who will be mounting a 6 layer PCB of size
>> 110x45mm on a shaft which will be rotating at 13000 rpm. The pcb is
>> mounted on a supporting plate with 3 -6 mounting points. He wanted our
>> suggestion on whether he can use normal FR4 or he should be going with a
>> metal core PCB. The board is 1.6mm thick.
>>
>> We felt that FR4 might be sufficient and the bond strength of the
>> components mounted on the board will be more critical than the PCB
>> tensile
>> strength. We felt since thermal management is not an issue in this case,
>> metal core may not be required. Will tensile strength of the board be a
>> critical parameter in this case and if so, any inputs on what can be
>> suggested. Any other suggestions for this application.
>>
>> Rgds
>>
>> Pradeep
>>
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