Like Bhanu says, its design dependent, tough to pin down on an IPC document. In my previous role with a board fabricator, I was familiar with many bare board designs that would hold up to 40 or more ‘ambient to 230C' cycles with less than a 5% change in resistance, from ‘as received', on coupons representing the build (IPC-TM-650 2.6.26A, Method B), indicative those boards could holdup to more than just a handful of reflows. On legacy designs, you may be limited by material of construction and whether legacy methods of fabrication are to be preserved on those builds.
José (Joey) Ríos, Sr QA Engineer
Mission Assurance Manager
Kavli Institute for Astrophysics & Space Research
Massachusetts Institute of Technology
[log in to unmask]<mailto:[log in to unmask]>
(617)324-6272
On Mar 28, 2018, at 2:41 PM, Nutting, Phil <[log in to unmask]<mailto:[log in to unmask]>> wrote:
Our reworks are not to a single location, but rather various cuts, jumpers and component changes. Some due to design issues of the existing board, change in operating points or obsolescence of the existing parts.
Only three reworks? Geesh, we surpassed that ages ago.
Having a magic number is easier for some folks to wrap their head around. I'll pass along your suggestions.
Thanks,
Phil
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of David Hillman
Sent: Wednesday, March 28, 2018 2:07 PM
To: [log in to unmask]<mailto:[log in to unmask]>
Subject: Re: [TN] when is there too much rework on a circuit board
Hi team! I agree with Bhanu, having a fixed number requires established processes and material sets to be safe and even then, there is risk. Our current procedures allow for 3 reworks before a process/design team consultation/review is required.
Dave Hillman
Rockwell Collins
[log in to unmask]<mailto:[log in to unmask]>
On Wed, Mar 28, 2018 at 1:03 PM, Bhanu Sood <[log in to unmask]> wrote:
Rework or scrap? the risk is usually assessed by weighing in the
laminate type (PI, FR-4, flex etc), design, board stack-up, components
in vicinity of rework site and time/temperature required for each
rework (including preheat).
Any guidelines regarding the number of allowable reworks are going to
be specific to a design/material combination, tricky to extrapolate
that guidance into a standard…rework risk assessment needs to analyze
all factors and be better understood with solid research. Most
companies say a site can be reworked 2 or 3 times (assuming high Td/Tg PI...$$$).
On Wed, Mar 28, 2018 at 1:40 PM, Nutting, Phil
<[log in to unmask]
wrote:
Respected colleagues,
I was just asked a question to which I could not put a number.
In the case of needing to fix a circuit board "right now" to fill
the income stream there should be a logical point at which the
reworks have become too extensive for production boards beyond the
"right now" need
and
the board should be revised to eliminate the reworks.
Is there an IPC or MIL standard that suggests a limit on the number
of or amount of rework allowed on a circuit board before it should be revised?
Phil Nutting | HVP Senior Development Engineer | Excelitas
Technologies Corp
Lab: +1 978.224.4332 | Office: +1 978.224.4152
35 Congress St, Salem, MA 01970 USA
[log in to unmask]<mailto:[log in to unmask]>
www.excelitas.com<http://www.excelitas.com/>
[Excelitas R_emailsig]
Please consider the environment before printing this e-mail.
________________________________
This email message and any attachments are confidential and
proprietary
to
Excelitas Technologies Corp. If you are not the intended recipient
of
this
message, please inform the sender by replying to this email or
sending a message to the sender and destroy the message and any
attachments. Thank you.
--
Bhanu Sood
Tel: (202) 468-8449
|
