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From:
"Decker, Scott UTAS" <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Decker, Scott UTAS
Date:
Wed, 15 Aug 2018 14:47:43 +0000
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Wayne,

    We have requirements here also regarding the location of MLCC's near the edges and areas of stress, like mounting holes, mouse bites, scoring, etc. and the electrical engineers are urged to use flexy leaded type caps when possible. Like Steve mentioned, .200" from a lot of things mentioned is a good start along with orientation of the components along the stress lines, etc. We also have restrictions on the soldering of boards with MLCC's on them as far as temp rise rate to avoid thermal shock. This is also related to the size and soldering type used, wave or re-flow. Something that might help also is to check into The Center For Advanced Life Cycle Engineering which is a research center at the University of Maryland. They have a calculator that you can use to help predict cracking issues with the parts. I can't share exact numbers and other related information without congressional approval from people I don't even know, but I will say that the .200" number is pretty good and Steve said the same thing. These parts have really been a thorn in the side for designs with always having to remember which way, and how far, etc. but it is what it is... :-/   Good luck.

Later...



Scott Decker – Staff Engineer, PCB Design Services CID+ – Electronic Systems Center

UTC AEROSPACE SYSTEMS

3445 S. 5th Street, Suite 170, Phoenix, AZ 85040 U.S.A.

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

From: TechNet [mailto:[log in to unmask]] On Behalf Of Wayne Thayer

Sent: Wednesday, August 15, 2018 6:22 AM

To: [log in to unmask]

Subject: Re: [TN] EXTERNAL: Re: [TN] MLCC spacing/orientation to V-score or Perforated Tabs



Hi Steve-



Thanks for the info. That sounds very reasonable, but it would be nice to have more analytical data such as -Which orientation is more susceptible to damage? (seems obvious with the tabs but I'm not certain on the scores) -It seems obvious that smaller parts would be less susceptible, so maybe they can be closer to the edge?



Wayne Thayer



On Tue, Aug 14, 2018 at 11:49 AM, Vargas, Stephen M < [log in to unmask]> wrote:



> Wayne:

>

>       We recommend keeping larger size ceramic style parts at least .200"

> from the PCB edge where depanelization is required. For V-Scores, we 

> ask that a route in the breakaway be added to minimizes the stresses. 

> For mouse-bites, we like to see the tabs as far as possible from the 

> edge parts.

>

> Regards,

> Steve Vargas

>

> Lockheed Martin RMS-Rotary and Mission Systems Polaris Contract Mfg.

> 15 Barnabas Rd

> Marion, MA 02738

> 774-553-6192

> [log in to unmask]

>

>  Please consider the environment before printing this e-mail

>

> -----Original Message-----

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

> Sent: Tuesday, August 14, 2018 2:36 PM

> To: [log in to unmask]

> Subject: EXTERNAL: Re: [TN] MLCC spacing/orientation to V-score or 

> Perforated Tabs

>

> That doesn't give me "warm fuzzies"! I have personally seen pizza 

> wheels result in a broken cap 0.125" away (no visual cue, 10% of parts 

> had the problem). Leaving a potential reliability issue to each pcb 

> assembly house is a real problem for me. And not just me, for all of 

> us who use PCBs. I did find a paper from Kemet which touched on the 

> issue, but not in any clear, useful guideline kind of way.

>

> Wayne Thayer

>

> On Tue, Aug 14, 2018 at 11:03 AM, John Maxwell <[log in to unmask]> wrote:

>

> > Depend on vendors recommendations for best results

> >

> > Sent from my iPad

> >

> > > On Aug 14, 2018, at 1:24 PM, Wayne Thayer <[log in to unmask]>

> > wrote:

> > >

> > > Hi-

> > >

> > > Is there an IPC standard for distances from components to board 

> > > edge for the V-score or perforated tab techniques? I've been able 

> > > to find several recommendations from manufacturers, but I couldn't 

> > > find the applicable

> > IPC

> > > doc.

> > >

> > > Wayne Thayer

> >

>


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