Victor,
To possibly disregard the 1.0 MM rule of thumb, ask your PCB Fab
manufacturers for crossection photos of their backdrilled holes,
particularly smaller holes. Also ask about their back-drill bit
geometry, and how quickly or well it removes material as it is cut.
There is no industry standard covering backdrilling in any great detail,
so board design engineers should work closely with their PCB suppliers
to determine the appropriate back-drill depth controls and limits. Note
that as back-drilling is becoming more common, many suppliers are still
on a learning curve concerning their backdrilling capability.
Regards,
Karl Sauter
On 7/1/2010 9:26 AM, [log in to unmask] wrote:
> Karl,
>
> How was the 0.1 mm value to the connecting or "Must Not Penetrate" layer determined? Do you have supporting documentation.? Can you share?
>
> "X"
>
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of Karl Sauter
> Sent: Thursday, July 01, 2010 9:59 AM
> To: [log in to unmask]
> Subject: Re: [TN] Single PCB backdrilling
>
> Chris,
>
> How reliable a back-drilled hole is depends upon how close the drilling gets to the "Must Not Penetrate" layer. The back-drill bit geometry, drilling parameters and hole size affect how much copper is pushed into the hole ahead of the tip and how much the PTH hole wall is stressed near the tip of the drill bit. A conservative rule of thumb is that the stressed area not be closer than 0.1 MM to the connecting or "Must Not Penetrate" layer.
>
> Regards,
> Karl Sauter
>
>
> On 7/1/2010 6:33 AM, Chris Mahanna wrote:
>
>> Backdrills are generally considered a unique structure for which structural integrity after thermal stress shall be assessed to prove conformance.
>> However, this is not 100% agreed upon and the specifications are rather mute/ambiguous.
>> Some procurement activities allow conformance assessment from simple electrical test of properly designed test coupons.
>>
>> I personally have not seen mandated reliability testing on backdrills. I suspect the lack of mandates indicates a general consensus that, in typical use, backdrills are more structurally reliable than their non-backdrilled counterparts.
>>
>> Chris
>>
>> -----Original Message-----
>> From: TechNet [mailto:[log in to unmask]] On Behalf Of ??
>> Sent: Thursday, July 01, 2010 12:01 AM
>> To: [log in to unmask]
>> Subject: [TN] Single PCB backdrilling
>>
>> Dear Technos,
>>
>> Anyone use backdrilling tech in a single pcb? We backdrilled a lot of backplanes, but none of them should survive a second reflow process and maybe a wave process.
>>
>> Here is the questions:
>>
>> Does the high temperature stress affect the backdrill holes reliability? Two reflow processes and a wave process, Consider the PTHs' drilled edge are rough, maybe they will easy to be damaged by thermal stress.
>>
>> Will the the rework process of the connector damage the backdrilled holes?
>>
>> Anything we can do? No HALS? More inner layer connection? Other suggestions?
>>
>> Thank you so much.
>>
>> B.R.
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Phone: +14082763207 <tel:+14082763207>
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Green Oracle <http://www.oracle.com/commitment> Oracle is committed to
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