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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