Wayne:
That is affirmative. SnPb is removed from everywhere except the
pads, lands and anything else that needs solder over the top of copper.
At this time bare copper is oxidized and needs to be cleaned by hand or
spray so that SMOBC can adhere to it and slivers brake off.
Ramon
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Wayne Thayer
Sent: Monday, May 07, 2007 8:56 AM
To: [log in to unmask]
Subject: Re: [TN] What is the difference between Fused SnPb and HASL?
Ramon-
What is it that needs mechanical removal? The oxidation of the copper
traces due to selective SnPb removal?
Wayne
>>> [log in to unmask] 5/7/2007 8:46 am >>>
Fused solder is more expensive and it takes about 5 more steps.
When the SnPb is used as etch resist, as Wayne mentions, to pattern the
outer layers and plate the pads and lands, the etching is not vertical
so there is some underetching.
slivers are formed at the top edge of the geometries. Later the traces
have the SnPb taken off. So prior to having the solder mask applied,
the copper traces are dull due to oxidation from etching the SnPb off
which needs to be mechanically removed, leaving possible inclusions
partially broken off. It can be a messy situation. Pads and lands are
left with the solder over them which is later on fused by reflow oven.
Thus the name fused solder. Most companies use HASL very few use Fused
solder.
Ramon
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Wayne Thayer
Sent: Monday, May 07, 2007 8:14 AM
To: [log in to unmask]
Subject: Re: [TN] What is the difference between Fused SnPb and HASL?
Werner is quite correct but only mentioned the metallurgy, not the
ramifications for processing.
HASL is a quite obnoxious process in terms of board stress during
application, but most non-aggressive board constructs can handle it:
The panel is plunged into a vat of molten solder and then withdrawn
while being blown off with very hot air. The deposits are lumpy, and
start giving problems for smaller parts.
Fused SnPb is just convection heated to slightly above the melting
point--no thermal shock. Also the deposits are extremely even, so
very
fine pitch work is no problem. However, the normal way of achieving
Fused SnPb is to use the plated SnPb for the final etch resist. This
means that if you have a board with a solder mask, then the SnPb will
be
under the mask, which will greatly reduce its effectiveness.
Wayne Thayer
>>> [log in to unmask] 5/6/2007 9:39 pm >>>
Hello,
I come across QML vendors that state their finish system : HASL, Fused
Solder, while some only states : HASL. I know that HASL stands for
"Hot
Air Solder Leveling", what then is fused solder? There must be some
difference between them - what are they?
Thanks and regards,
Wee Mei
---------------------------------------------------
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
-----------------------------------------------------
---------------------------------------------------
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
-----------------------------------------------------
|
