Thanks for the very detailed reply Richard,
I had just one board where 4 BGAs were needed to be replaced on it. I applied tacky flux to the pads manually (to hold BGAs in place) and had the placement machine put them on and then sent the assembly thru the oven. The only difference between these 4 BGAs and the other 14 BGAs was increased voiding in the 4 that were put down this way. All the other BGAs looked the same under X-Ray after 1st and 2nd reflow.
Are you saying the components should be fluxed regardless of whether or not they are being reflowed for the first time?
Amol
-----Original Message-----
From: Stadem, Richard D. [mailto:[log in to unmask]]
Sent: Thursday, August 09, 2007 8:51 AM
To: TechNet E-Mail Forum; Kane, Amol (349)
Subject: RE: [TN] Rework question
Hi, Amol
Yes, you are missing flux.
You can reflow the entire board, but you somehow need to add flux to get
good solder joints. This means under those BGAs as well. But it does
make sense to do so rather than subject the entire assembly to the
pre-heat several times, and with localized heating several times as
well.
First of all, was the board originally processed with no-clean flux? If
so, you need to remove the residues. You cannot achieve good solder
joints with the original no-clean flux still on the solder joints.
But if the assemblies were originally reflowed with water-soluble pastes
and wire solder, and no no-clean flux was used, you are past the first
hurdle.
Next evaluate for the presence of components that were added after the
reflow process, such as trimpots, UV90 connectors, through-hole parts,
etc, that cannot withstand the reflow temperatures. These will need to
be removed.
Then very lightly spray a water-soluble liquid flux such as Kester
2331ZX over the assembly using a fine-mist spray bottle. Using an air
hose, blow the flux under the BGAs, then blow off all excess flux from
the entire assembly. Make sure there is not too much flux anywhere, but
especially under the BGAs or it will cause the solderballs to wick
together from the capillary action.
Then reflow the second time, followed by two passes through the wash to
make sure all of the flux is removed.
Do one board, inspect it 100%. Inspect it in the X-ray. After the double
wash do an Ionograph or Omegameter check to make sure there is no change
in the cleanliness levels. Re-test it to ensure no test issues are seen.
If everything checks out, do a lot of 5 and repeat all the process
control checks. Everything still OK? Then do 10 and continue to check
everything. If no problems pop up then finish the lot.
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Kane, Amol (349)
Sent: Wednesday, August 08, 2007 9:57 AM
To: [log in to unmask]
Subject: Re: [TN] Rework question
A tangent to the original question on rework...........what are
arguments for and against reflowing an entire assembly (putting it thru
the reflow oven again) instead of reworking say 4 or 5 BGAs on the same
board by traditional BGA rework equipment?
True, all the other components (including the good BGAs) will undergo
one more reflow....but are there studies/literature out there that
suggest that this induces failures among earlier good and working
components?
If there is a choice between subjecting the board to 4X2=8 thermal
cycles for removal and replacement of the 4 BGAs (scrapping the board is
not an option), reflowing the entire assembly once makes sense.
Am I missing some important consideration/s here?
Thanks,
Amol
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of David D. Hillman
Sent: Wednesday, August 08, 2007 10:45 AM
To: [log in to unmask]
Subject: Re: [TN] Rework question
Hi gang! As many folks have pointed out, there is no IPC
guideline/specification that contains a maximum rework limit value. I
have two additional considerations when attempting to create a maximum
rework limit value - the laminate Tg in relation to the solder process
and the laminate CTE value above the Tg value (typically designated as
alpha 2).
If your soldering process exceeds the laminate Tg then you are inducing
a significant amount of stress on pwa structures such as pads, traces,
and plated thru holes - the higher the laminate Tg value, the lower the
amount of induced stress (or alternatively, a soldering process
temperature below the laminate Tg would be good). Also, if the CTE value
above the Tg is high, then the time duration above the Tg for the rework
process should be minimized as much as possible. The pwa laminate is a
critical consideration of the maximum rework limit value thus the reason
for not finding an IPC recommendation - "it depends" on the laminate
used.
And Dewey - handing Doug a soldering iron is like asking me to spray
conformal coating - a really bad idea!
Dave Hillman
Rockwell Collins
[log in to unmask]
"Whittaker, Dewey (EHCOE)" <[log in to unmask]> Sent by:
TechNet <[log in to unmask]>
08/07/2007 01:22 PM
Please respond to
TechNet E-Mail Forum <[log in to unmask]>; Please respond to "Whittaker,
Dewey (EHCOE)" <[log in to unmask]>
To
[log in to unmask]
cc
Subject
Re: [TN] Rework question
Excellent points made by Bev and yourself and I concur. The answer to
one of the initial questions was whether there were a different number
of reworks allowed if it was a Lead-free process or not. For the
Aerospace Industry, if and when we are Lead-free the assemblies will
have to be equal to or better than the current leaded processes, so
there would be no difference in the reworks allowed.
As a precursor to that happening our laminate materials we specify now
are already being tested to those processing conditions and end use
environments. The designs are robust enough that there is no potential
limit to the number of thermal excursions they can experience under
controlled conditions. I have tried to make the printed boards
bullet-proof so no matter who it is outsourced to for the assembly
portion, they will meet the expected performance requirements. They
should even tolerate being soldered by Doug Pauls.
Dewey
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Stadem, Richard D.
Sent: Tuesday, August 07, 2007 10:59 AM
To: [log in to unmask]
Subject: Re: [TN] Rework question
I thought so. How could something like that be applied, as Bev correctly
pointed out. There are too many variables that would determine the
number of "safe" reworks.
I prefer the term "Tg excursions" when a rework limit is set on
agreement with customer and supplier. And a careful qualification is
needed, as Bev pointed out, and it is usually a worthwhile effort to do
so. Solder touchup and hand-soldering are usually excluded from this
number, as this type of rework seldom leads to reliability issues. But
again, there are exceptions.
In addition to having "seen thin boards delaminated after a single, poor
attempt at rework" I have also seen any given size and thickness and
material type delaminated in spite of very careful qualification of the
rework process. Also, I have seen Z-axis expansion as a result of too
large of a delta T between the localized rework site and the rest of the
assembly cause damage to vias and PTH barrels that went totally
undetected by a careful inspection and X-ray and electrical test,
including stress screening, only to fail later.
This is why the hard limitation of the number of reworks was deleted
when the standards changed from WS6536E, to J-STD-2000, to today's
J-STD-001D and IPC-A-610D. There is no number of Tg excursions that is
"safe" for every application.
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Bev Christian
Sent: Tuesday, August 07, 2007 12:09 PM
To: [log in to unmask]
Subject: Re: [TN] Rework question
Same here.
Bev
RIM
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of John Burke
Sent: Tuesday, August 07, 2007 12:55 PM
To: [log in to unmask]
Subject: Re: [TN] Rework question
Just looked in 7711 - didn't see a reference to it...
John
John Burke
(408) 515 4992
-----Original Message-----
From: Guy Ramsey [mailto:[log in to unmask]]
Sent: Tuesday, August 07, 2007 9:14 AM
To: 'TechNet E-Mail Forum'; 'John Burke'
Subject: RE: [TN] Rework question
I don't think it is worded as a hard limit. Might be IPC-7711.
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of John Burke
Sent: Tuesday, August 07, 2007 12:04 PM
To: [log in to unmask]
Subject: Re: [TN] Rework question
The question actually came up because there is stated (somewhere?) in an
IPC document the number of reflow cycles you are allowed to put the
board through.
Taking that limit into account (first side reflow, second side etc)
allowed them to remove and replace the same component 3 times in a worst
case scenario.
And I agree with Bev the whole thing is open to interpretation as to
what represents a reflow cycle - pad dressing removal etc.
John Burke
(408) 515 4992
-----Original Message-----
From: Bev Christian [mailto:[log in to unmask]]
Sent: Tuesday, August 07, 2007 8:53 AM
To: TechNet E-Mail Forum; John Burke
Subject: RE: [TN] Rework question
John,
I am having people look, but if there is a limit I do not remember.
However, from a practical point of view, the answer is Doug Pauls'
patented (Or is that copyrighted or trade marked? Being a lawyer, I
don't
know.) phrase, "It all depends". It depends on the method of rework,
(reflow, wave solder, selective soldering, soldering iron, hot air gun
focused IR, flame), temperatures reached, ramp rates, dwells, size of
board, thickness of board, type of component, heat sinks, skill of
operator. I could go on. Make yourself a fishbone diagram.
And then are we talking about say 3X of the same component, or 5X
side-by-side or 7x but each in a thermally separated area from the other
six?
Here's a scenario for you: double sided reflow and then required rework
under cans on both sides of the board. So this means two more for can
removal, dressing the can pads, removing the components, dressing the
pads, part deposition, can replacement. And hope everything works!
So you need visual inspection, x-ray inspection, electrical test and if
you really want to do it right, x-sectioning and a whole battery of
reliability testing.
I have seen good work and I have seen thin boards delaminated after a
single, poor attempt at rework.
Bev
RIM
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of John Burke
Sent: Tuesday, August 07, 2007 10:29 AM
To: [log in to unmask]
Subject: [TN] Rework question
Hi,
I had a question yesterday which was "has the number of re-work cycles
allowed by IPC changed for lead free?"
And I confess I don't know but I bet someone on this link does.
If you could let me know number of thermal cycles allowed and the spec
reference I would be grateful.
John
John Burke
(408) 515 4992
---------------------------------------------------
Technet Mail List provided as a service by IPC using LISTSERV 15.0 To
unsubscribe, send a message to [log in to unmask] with following text in
the BODY (NOT the subject field): SIGNOFF Technet To temporarily halt or
(re-start) delivery of Technet send e-mail to
[log in to unmask]: SET Technet NOMAIL or (MAIL) To receive ONE mailing
per day of all the posts: send e-mail to
[log in to unmask]: SET Technet Digest
Search the archives of previous posts at:
http://listserv.ipc.org/archives
Please visit IPC web site
http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for additional
information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100
ext.2815
-----------------------------------------------------
---------------------------------------------------------------------
This transmission (including any attachments) may contain confidential
information, privileged material (including material protected by the
solicitor-client or other applicable privileges), or constitute
non-public information. Any use of this information by anyone other than
the intended recipient is prohibited. If you have received this
transmission in error, please immediately reply to the sender and delete
this information from your system. Use, dissemination, distribution, or
reproduction of this transmission by unintended recipients is not
authorized and may be unlawful.
---------------------------------------------------
Technet Mail List provided as a service by IPC using LISTSERV 15.0 To
unsubscribe, send a message to [log in to unmask] with following text in
the BODY (NOT the subject field): SIGNOFF Technet To temporarily halt or
(re-start) delivery of Technet send e-mail to [log in to unmask]: SET
Technet NOMAIL or (MAIL) To receive ONE mailing per day of all the
posts: send e-mail to [log in to unmask]: SET Technet Digest Search the
archives of previous posts at: http://listserv.ipc.org/archives Please
visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for
additional information, or contact Keach Sasamori at [log in to unmask] or
847-615-7100
ext.2815
-----------------------------------------------------
---------------------------------------------------
Technet Mail List provided as a service by IPC using LISTSERV 15.0 To
unsubscribe, send a message to [log in to unmask] with following text in
the BODY (NOT the subject field): SIGNOFF Technet To temporarily halt or
(re-start) delivery of Technet send e-mail to
[log in to unmask]: SET Technet NOMAIL or (MAIL) To receive ONE mailing
per day of all the posts: send e-mail to
[log in to unmask]: SET Technet Digest
Search the archives of previous posts at:
http://listserv.ipc.org/archives
Please visit IPC web site
http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for additional
information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100
ext.2815
-----------------------------------------------------
---------------------------------------------------------------------
This transmission (including any attachments) may contain confidential
information, privileged material (including material protected by the
solicitor-client or other applicable privileges), or constitute
non-public information. Any use of this information by anyone other than
the intended recipient is prohibited. If you have received this
transmission in error, please immediately reply to the sender and delete
this information from your system. Use, dissemination, distribution, or
reproduction of this transmission by unintended recipients is not
authorized and may be unlawful.
---------------------------------------------------
Technet Mail List provided as a service by IPC using LISTSERV 15.0 To
unsubscribe, send a message to [log in to unmask] with following text in
the BODY (NOT the subject field): SIGNOFF Technet To temporarily halt or
(re-start) delivery of Technet send e-mail to [log in to unmask]: SET
Technet NOMAIL or (MAIL) To receive ONE mailing per day of all the
posts: send e-mail to [log in to unmask]: SET Technet Digest Search the
archives of previous posts at: http://listserv.ipc.org/archives Please
visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for
additional information, or contact Keach Sasamori at [log in to unmask] or
847-615-7100 ext.2815
-----------------------------------------------------
---------------------------------------------------
Technet Mail List provided as a service by IPC using LISTSERV 15.0 To
unsubscribe, send a message to [log in to unmask] with following text in
the BODY (NOT the subject field): SIGNOFF Technet To temporarily halt or
(re-start) delivery of Technet send e-mail to
[log in to unmask]: SET Technet NOMAIL or (MAIL) To receive ONE mailing
per day of all the posts: send e-mail to
[log in to unmask]: SET Technet Digest
Search the archives of previous posts at:
http://listserv.ipc.org/archives
Please visit IPC web site
http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for additional
information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100
ext.2815
-----------------------------------------------------
---------------------------------------------------
Technet Mail List provided as a service by IPC using LISTSERV 15.0 To
unsubscribe, send a message to [log in to unmask] with following text in
the BODY (NOT the subject field): SIGNOFF Technet To temporarily halt or
(re-start) delivery of Technet send e-mail to
[log in to unmask]: SET Technet NOMAIL or (MAIL) To receive ONE mailing
per day of all the posts: send e-mail to
[log in to unmask]: SET Technet Digest
Search the archives of previous posts at:
http://listserv.ipc.org/archives Please visit IPC web site
http://www.ipc.org/contentpage.asp?Pageid=4.3.16
for additional information, or contact Keach Sasamori at [log in to unmask]
or 847-615-7100 ext.2815
-----------------------------------------------------
---------------------------------------------------
Technet Mail List provided as a service by IPC using LISTSERV 15.0 To
unsubscribe, send a message to [log in to unmask] with following text in
the BODY (NOT the subject field): SIGNOFF Technet To temporarily halt or
(re-start) delivery of Technet send e-mail to [log in to unmask]: SET
Technet NOMAIL or (MAIL) To receive ONE mailing per day of all the
posts: send e-mail to [log in to unmask]: SET Technet Digest Search the
archives of previous posts at: http://listserv.ipc.org/archives Please
visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for
additional information, or contact Keach Sasamori at [log in to unmask] or
847-615-7100 ext.2815
-----------------------------------------------------
CONFIDENTIALITY NOTICE:
This e-mail, and any attachments, is for the sole use of the intended
recipient(s) and may contain information that is confidential and
protected from disclosure under the law. Any unauthorized review, use,
disclosure, or distribution is prohibited. If you are not the intended
recipient, please contact the sender by reply e-mail, and delete/destroy
all copies of the original message and attachments.
Thank you.
---------------------------------------------------
Technet Mail List provided as a service by IPC using LISTSERV 15.0 To
unsubscribe, send a message to [log in to unmask] with following text in
the BODY (NOT the subject field): SIGNOFF Technet To temporarily halt or
(re-start) delivery of Technet send e-mail to [log in to unmask]: SET
Technet NOMAIL or (MAIL) To receive ONE mailing per day of all the
posts: send e-mail to [log in to unmask]: SET Technet Digest Search the
archives of previous posts at: http://listserv.ipc.org/archives Please
visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for
additional information, or contact Keach Sasamori at [log in to unmask] or
847-615-7100 ext.2815
-----------------------------------------------------
CONFIDENTIALITY NOTICE:
This e-mail, and any attachments, is for the sole use of the intended
recipient(s) and may contain information that is confidential and
protected from disclosure under the law. Any unauthorized review, use,
disclosure, or distribution is prohibited. If you are not the intended
recipient, please contact the sender by reply e-mail, and delete/destroy
all copies of the original message and attachments.
Thank you.
---------------------------------------------------
Technet Mail List provided as a service by IPC using LISTSERV 15.0
To unsubscribe, send a message to [log in to unmask] with following text in
the BODY (NOT the subject field): SIGNOFF Technet
To temporarily halt or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL)
To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest
Search the archives of previous posts at: http://listserv.ipc.org/archives
Please visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100 ext.2815
-----------------------------------------------------
|
