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July 2010

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Subject:
From:
Paul Reid <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Paul Reid <[log in to unmask]>
Date:
Fri, 2 Jul 2010 07:45:08 -0400
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text/plain (181 lines)
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
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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!


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