it's a trap. Paul's trying to raise funds to paint Bill Birch's
parking space in a paisley pattern.

At 04:45 AM 7/2/2010, Paul Reid wrote:
>Hi Li Yi,
>
>We have specifically designed reliability test coupons some of which
>include back drill holes. There is no limit imposed by our testing
>to hole size, back drill holes size, grid size, layer count etc. We
>would test about 100 to 200 holes in a circuit with two or three
>circuits per coupon. At least one of our coupon designs have both
>PTH and back drilled PTH in the same coupon.
>
>We usually have to design a custom coupon for each application. We
>would design a coupon that has the must break layers and must keep
>layer so we can beep out the circuits and demonstrate the coupons,
>and by implication the boards, are drilled correctly.
>
>I will continue this conversation with you off line.
>
>
>Sincerely,
>Paul Reid
>
>Program Coordinator
>PWB Interconnect Solutions Inc.
>235 Stafford Rd., West, Unit 103
>Nepean, Ontario
>Canada, K2H 9C1
>613 596 4244 ext. 229
>Skype paul_reid_pwb
>[log in to unmask] <mailto:[log in to unmask]>
>
>
>-----Original Message-----
>From: TechNet [mailto:[log in to unmask]] On Behalf Of ??
>Sent: July 1, 2010 9:39 PM
>To: [log in to unmask]
>Subject: Re: [TN] Single PCB back drilling
>
>Thanks to all of you, Paul, Chris, Karl and Reuven
>
>Got it, a correctly design and backdrilled hole sacrifices no
>reliability issues but maybe a more reliable one due to stress relief.
>
>Maybe a wording mistake, we hadn't gotten a failure by now. For all
>the backdrilling holes were located on backplanes who need no high
>temperature process. No sign of rework and thermal failures were
>found.So the matter we are discussing is not really a design disaster :)
>
>Depends on my PCB fab's capability, a 0.2mm safe depth should be
>kept towards the "must keep layer", the backdrill diameter is
>0.2mm-0.25mm larger than the original one. Those DFM rules influent
>the maximum stub length which had been considered by our SI
>Engineers. The less no function pads be kept in high speed circuits
>the better, I still think one more pad should be kept below the
>"must kept layer" though they maybe less reliable in T-C tests,to
>keep more mechanical anti-pulling force in connector rework process:
>-- --Top Pad
>-- --high speed layer pad
>-- --None function pad
>
>Paul, could you please send me your backdrilling capability? Some
>vias whose diameter are 10mil or less need be backdrilled (under the
>BGA), are there any of your customers have those requirements before?
>
>Many more thanks.
>
>B.R.
>~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>Li Yi
>H3C R&D DFM Engineer
>312 Room, Oriental Electronics Bldg., Shangdi Information
>Industry Base, Haidian District, Beijing, PRC(100085)
>Tel: 8610 82774692
>Fax:8610 82774214
>www.H3C.com
>~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>Causion:
>This e-mail and its attachments contain confidential information
>from H3C, which is intended only for the person or entity whose
>address is listed above. Any use of the information contained herein
>in any way (including, but not limited to, total or partial
>disclosure, reproduction, or dissemination) by persons other than
>the intended recipient(s) is prohibited. If you receive this e-mail
>in error, please notify the sender by phone or email immediately and delete it!
>----- Original Message -----
>From: "Paul Reid" <[log in to unmask]>
>To: <[log in to unmask]>
>Sent: Friday, July 02, 2010 4:54 AM
>Subject: Re: [TN] Single PCB back drilling
>
>
>Hi Li Yi,
>
>We perform reliability testing on representative coupons from back
>drilled printed wire boards frequently. If the back drilling is
>performed correctly, it will significantly extend the reliability of
>the board. It is rare that reliability failures occur in PTHs that
>have back drill. The only failure I remember on a back drilled hole
>was when the drill touched the layer that was part of the test
>circuit. The coupon passed electrical test but failed almost
>immediately when thermal cycled.
>
>It appears that by removing the barrel and connection to the surface
>pad and some internal interconnections, the PTH is stress relieved.
>When we test coupons that have PTHs with and without back drilling
>in the same coupon, failures occur first on the holes that are not
>back drilled. Base on testing we have done hole size does not appear
>to be influential on back drill reliability.
>
>If back drilling is performed to the correct depth, and with good
>registration, then I expect that the problem you are seeing is
>coincidental to the back drilling.
>
>I would not have non-functional pads present. Generally that does
>not improve reliability based on thermal cycle testing.
>
>Can you post a microsection of the failure mode?
>
>
>Sincerely,
>Paul Reid
>
>Program Coordinator
>PWB Interconnect Solutions Inc.
>235 Stafford Rd., West, Unit 103
>Nepean, Ontario
>Canada, K2H 9C1
>613 596 4244 ext. 229
>Skype paul_reid_pwb
>[log in to unmask] <mailto:[log in to unmask]>
>
>
>-----Original Message-----
>From: TechNet [mailto:[log in to unmask]] On Behalf Of ??
>Sent: July 1, 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.
>~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>Li Yi
>H3C R&D DFM Engineer312 Room, Oriental Electronics Bldg., Shangdi Information
>Industry Base, Haidian District, Beijing, PRC(100085)
>Tel: 8610 82774692
>Fax:8610 82774214
>www.H3C.com
>~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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>This e-mail and its attachments contain confidential information
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>
>
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