Like you, it was never old, and never will be.
-----Original Message-----
From: John Maxwell [mailto:[log in to unmask]]
Sent: Wednesday, August 15, 2018 1:30 PM
To: TechNet E-Mail Forum; Stadem, Richard D
Subject: Re: [TN] EXTERNAL: Re: [TN] MLCC spacing/orientation to V-score or Perforated Tabs
I have been out for a couple of day and am now enjoying the thread. I did not know that the .200” spacing in in IPC 2221but I published that was a good number in an AVX app note titled “Cracks There Hidden Defect” in August 1987. It just shows how old I am to see the discussion 31 years later. What was old is now new again:-)
John Maxwell
> On Aug 15, 2018, at 1:40 PM, Stadem, Richard D <[log in to unmask]> wrote:
>
> Yes and that is done, but the drawback is that you are now dealing with the FR-4 dust in the assembly factory, and there is a cost in that it is considered hazardous.
>
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of Robert Kondner
> Sent: Wednesday, August 15, 2018 12:37 PM
> To: [log in to unmask]
> Subject: Re: [TN] EXTERNAL: Re: [TN] MLCC spacing/orientation to V-score or Perforated Tabs
>
> Riding a metro bus down the side of a PCB will induce strain as well, not the fault of the bus but maybe the operator.
>
> Can a V Score machine be used to completely cut through a PCB like the Fancort VPD machine mentioned? That seems like pretty low stress over the board.
>
> Bob K.
>
> -----Original Message-----
> From: TechNet <[log in to unmask]> On Behalf Of Drew meyer
> Sent: Wednesday, August 15, 2018 12:36 PM
> To: [log in to unmask]
> Subject: Re: [TN] EXTERNAL: Re: [TN] MLCC spacing/orientation to V-score or Perforated Tabs
>
> Wayne,
>
> We have used the pizza cutter style as well and it can induce some strain on the board, more than you might think possible. The depth of the V-score can vary and the wheels may not track exactly down the middle of the V-score. In one case the V-score depth varied enough that the wheel walked out of the groove and into the PCB. Scrap that panel!!!!
>
> A well maintained router is the best method. But as you can see above, even here it is not applied to every product.
>
> Drew
>
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of Wayne Thayer
> Sent: Wednesday, August 15, 2018 10:20 AM
> To: [log in to unmask]
> Subject: Re: [TN] EXTERNAL: Re: [TN] MLCC spacing/orientation to V-score or Perforated Tabs
>
> Thanks Scott.
>
> I'll see what I can divine from CALCE.
>
> I have a hard time imagining the "stress lines" for the V-score (aka "Pizza
> Wheel") singulation process. With tabs, bending is clearly the way shock waves propagate, so you'd think aligning parts with the long access parallel to the edge would be the orientation for minimal differential stress. But the "Pizza Wheel" is trying to rip the board apart in a very different way. I'm suspecting the stress waves would be of similar shape to the waves around the bow of a canoe when you're moving through the water:
> They start out as propagating in the same direction as the bending waves, but end up turning nearly 90 degrees as the wheel wedges the board apart.
> Probably CALCE has modeled that.
>
> Wayne Thayer
>
> On Wed, Aug 15, 2018 at 7:47 AM Decker, Scott UTAS < [log in to unmask]> wrote:
>
>> 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.
>> Tel: 602 308 5957 FAX: 602 243 2347
>> KE7MWT AKA:PadMasterson
>> [log in to unmask] www.utcaerospacesystems.com
>>
>> CONFIDENTIALITY WARNING: This message may contain proprietary and/or
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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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