Victor,
As an independent lab running these two methods side-by-side for about 3 years now, I can tell you there is very little user-side risk to switching to 2.6.27. There is however, substantial relative risk to staying with 2.6.8 (or wave, as you ask).
With respect to soldering thermal excursion induced failures, the 80/20 rule always boils-down to barrel cracks and post sep.
In general, 2.6.8 does not induce barrel cracks, regardless of # of cycles, while 2.6.27 is surprisingly good at it. We have not seen a 2.6.27 induced crack be classified as a false non-conformance.
Of course you can parlay this into 2.6.27 + 2.6.7.2 (as PCQRR has for years), just be sure to define the number of 2.6.27 cycles!
On the other hand, 2.6.27 does induce post-sep. You just have to be ready with the competence and fortitude to call a less-ugly separation.
My suggestion is to move to 2.6.27 as soon as feasible. IMO, do not paint yourself in a corner by forcing the stress of entire parts. 2.6.27 tolerances were designed for coupons! It is sometimes physically impossible to get an entire part to meet the profile in forced convection, regardless of the oven.
An aerospace prime recently released a drawing note of minimum excision size (not sure I should say what the size is) for DPA work against 2.6.27. I see this as very reasonable and a likely winner in the industry debate on the issue. To my knowledge, such excisions have always been acceptable for 2.6.8 work.
Hope this helps.
Chris
Chris Mahanna
Robisan Lab
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Victor Hernandez
Sent: Tuesday, June 07, 2011 11:35 AM
To: [log in to unmask]
Subject: [TN] PCB/PWB - Thermal Stress - Solder Float - TM650, 2.6.8
Fellow TechNetters:
I apologize for multiple post of this inquiry. I have had no feedback on and would definitely like to have some sort of dialogue on the topic.
Victor,
-----Original Message-----
From: Hernandez, Victor G
Sent: Monday, June 06, 2011 2:14 PM
To: Joyce Koo
Cc: Hernandez, Victor G
Subject: FW: PWB - Thermal Stress - TM650, 2.6.8
Joyce,
Any thoughts on this scenario.
Victor,
-----Original Message-----
From: Hernandez, Victor G
Sent: Monday, June 06, 2011 12:24 PM
To: TechNet E-Mail Forum
Cc: Hernandez, Victor G
Subject: PWB - Thermal Stress - TM650, 2.6.8
Fellow TechNetters:
How valid would it be to send an entire board, 16X19x0.094 inches, through the wave solder process x number of times, 1x, 2x, 3x, etc., and call it thermal stress. Also the extracted coupon size are ¾ x 1/2 inches removed with a router . What are the Pros and Cons with this method of thermal stress in accordance with IPC guidelines.
"X"
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