Agree. Some of the QFN or QFP could have molding compound on the
leadframe, prohibit the wetting of solder. Mold breed sometimes also
cause solderability problems. I have to admit, as long as you stay with
components from brand name, you do not have too much of problem.
(Haven't see the contaminated leads for years now. But is you do, run
like hell).
jk
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of David D. Hillman
Sent: Thursday, April 01, 2010 9:41 PM
To: [log in to unmask]
Subject: Re: [TN] Lead forming angle and solder joint formation
Hi folks - one more possible root cause - poor solderability of the QFP
either due to surface finish or lead forming operation.
Dave Hillman
Rockwell Collins
[log in to unmask]
Werner Engelmaier <[log in to unmask]>
Sent by: TechNet <[log in to unmask]>
03/31/2010 03:01 PM
Please respond to
TechNet E-Mail Forum <[log in to unmask]>; Please respond to
Werner Engelmaier <[log in to unmask]>
To
[log in to unmask]
cc
Subject
Re: [TN] Lead forming angle and solder joint formation
Hi Amol,
Not having a heel fillet can be a problem?but not likely for a
fine-pitch
QFP.
Your causes of not having a heel fillet could be (1) there is no
soldering
pad at the heel bend (you saying you have near-vertical leads could be a
clue); (2) your peak reflow temperature is too low (the component die is
a
heat sink and the leads are quite a bit cooler than the PCB pad); (3)
not
enough solder paste.
Werner
-----Original Message-----
From: Kane, Amol (349) <[log in to unmask]>
To: [log in to unmask]
Sent: Wed, Mar 31, 2010 3:24 pm
Subject: [TN] Lead forming angle and solder joint formation
I have had a very similar as Bev issue come up here, only in this case
it
has to
do with the absence of a heel fillet on a completely plated part. My
question is
this: Does the lead forming angle play a role in whether or not a heel
fillet
forms when a part is soldered to the pad?
We have a fine pitch QFP device (19 mil pitch) that we are soldering at
SMT. Our
quality department is rejecting the boards because of a absence of a
visible
heel fillet per IPC 610D class 3. When I look at an unsoldered part
under
the
scope, the angle between the foot and the leg is damn close to 90
degrees!
We are using a 5 mil thick stencil with 1 mil reduction on the width and
1:1 in
the length, resulting in a 2-3 mil actual solder height (after the flux
has
blown off). Has anyone seen a scenario that prevents the solder from
wicking up
the foot to the leg forming a heel fillet because of the forming angle?
I
am
also looking to see if a possible contamination issue on the part can
result in
this phenomenon.
Thanks,
Amol
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Bev Christian
Sent: Tuesday, March 30, 2010 9:24 PM
To: [log in to unmask]
Subject: Re: [TN] Need some opinions
Dave,
A distinction has to be made between failing the SMT process and failing
the
product. Obviously the issue has little to do with screen printing,
placement or reflow - all other parts have the proper amount of solder
paste, are placed properly, have good looking joints and intermetallic
of
an
appropriate thickness is there, even on the leaded component in question
(where there is an actual joint!). So the process is in control.
With regards to the two other component types, I have some comments.
SOIC
sheared toes have been a pain for quite some time. However, we already
know
that toe fillets only provide 5% of joint strength at most and industry
available reliability data certainly shows that absence of toe fillets
on
leaded components is not something to be overly concerned about. OK,
let's
discuss LGAs and QFNs with sawn vertical surfaces.
1) The easiest way to avoid bulbous joints with these components
is
tight control of pad size and the amount of solder paste deposited.
2) If negative wetting angles are produced, they are not pointed
in
the direction where it can do the most damage. They point straight down
into the bulk of the solder. Negative wetting angles at the heel fillet
of
a leaded device are pointing right down or close to the intermetallic
demarcation line.
3) We have never seen a bulbous joint of a LGA or QFN on a rigid
board
cause a failure during thermal cycling, drop or tumble.
4) However, we do not allow bulbous joints on these devices on
flex
circuits. I'll let everyone think about that one. Maybe we are over
cautious, but.
Bev
RIM
_____
From: [log in to unmask] [mailto:[log in to unmask]]
Sent: Tuesday, March 30, 2010 5:30 PM
To: TechNet E-Mail Forum; Bev Christian
Cc: [log in to unmask]
Subject: Re: [TN] Need some opinions
Hi Bev - I wouldn't "fail" the soldering process or the solder joint if
I
can show the reason is the lack of plating "by design" as you described.
However, as other folks have pointed out, there are other functional
issues
having a SMT component lead sufficiently plated which need to be
considered.
The industry is already starting to ask the same questions in terms of
have
sheared toes (SOIC type components) or sawed surfaces (QFN type
components)
but those cases are not as severe as your case.
Dave Hillman
Rockwell Collins
[log in to unmask]
Bev Christian <[log in to unmask]>
Sent by: TechNet <[log in to unmask]>
03/25/2010 08:08 PM
Please respond to
TechNet E-Mail Forum <[log in to unmask]>; Please respond to
Bev Christian <[log in to unmask]>
To
[log in to unmask]
cc
Subject
[TN] Need some opinions
Technetters,
It seems that more and more component suppliers are not plating their
leads
all the way up to the component body. In fact some are getting downright
skimpy and only plating to the bottom bend, never mind the upper one. If
you
put down a lot of solder paste you end up with a bulbous joint, a
negative
wetting angle and a stress concentration point. If you put down less
paste
and have a co-planarity issue, then you have the potential for opens.
The
other option of course is getting the supplier to plate higher up the
leads.
Question: would you consider the condition of the formation of the
negative
wetting angles a failure during process qualification?
Bev
RIM
______________________________________________________________________
This email has been scanned by the MessageLabs Email Security System.
For more information please contact helpdesk at x2960 or
[log in to unmask]
______________________________________________________________________
---------------------------------------------------
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 email has been scanned by the MessageLabs Email Security System.
For more information please contact helpdesk at x2960 or
[log in to unmask]
______________________________________________________________________
---------------------------------------------------
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
-----------------------------------------------------
WARNING: Export Control
This document may contain technical data within the definition of the
International Traffic in Arms Regulations (ITAR), and subject to the
Export
Control Laws of the U.S. Government. Transfer of such data by any means
to a
foreign person, whether in the United States or abroad, without proper
export
authorization or other approval from the U.S. Department of State is
prohibited.
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.
______________________________________________________________________
This email has been scanned by the MessageLabs Email Security System.
For more information please contact helpdesk at x2960 or
[log in to unmask]
______________________________________________________________________
---------------------------------------------------
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 email has been scanned by the MessageLabs Email Security System.
For more information please contact helpdesk at x2960 or
[log in to unmask]
______________________________________________________________________
---------------------------------------------------
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 email has been scanned by the MessageLabs Email Security System.
For more information please contact helpdesk at x2960 or
[log in to unmask]
______________________________________________________________________
---------------------------------------------------
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.
______________________________________________________________________
This email has been scanned by the MessageLabs Email Security System.
For more information please contact helpdesk at x2960 or [log in to unmask]
______________________________________________________________________
---------------------------------------------------
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
-----------------------------------------------------
|
