Ramon
Normally, HASL is the less expensive alternative and thinner. Consequently by being thinner, it may produce a smaller meniscus which is usually an advantage. The risk here though is solderability; the thinner the solder the more likely the occurrence of surface intermetallics. These issues have been the focus of engineering attention for years and have become more acute as the feature sizes diminished. This is why the the industry is migrating from HASL to hard metal finishes.
Best regards
Lee
J. Lee Parker, Ph.D.
JLP Consultants LLC
804 779 3389
----- Original Message -----
From: Dehoyos, Ramon<mailto:[log in to unmask]>
To: [log in to unmask]<mailto:[log in to unmask]>
Sent: Tuesday, October 11, 2005 4:20 PM
Subject: Re: [TN] Hasl
Thanks Dr Parker and Richard for your inputs. Comparing SSSR and
HASL final plating which are made both using eutectic Tin/Lead solder
and other Lead free materials, the end surface is still domed in the
middle. So both have weak gasketing due to their lack in flatness.
Setting this issue aside, what are the advantages of one versus the
other besides the longer shelf life of SSSR.
Regards,
Ramon
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Stadem, Richard
Sent: Tuesday, October 11, 2005 2:03 PM
To: [log in to unmask]<mailto:[log in to unmask]>
Subject: Re: [TN] Hasl
The idea of the flat surface finish is for both stencil gasketing to the
board and for placement accuracy. To form a "perfect brick" of solder
paste, there has to be a certain amount of pressure (a lot less than
most people think). To prevent squeezout of paste between stencil and
board, there has to be good, really good, gasketing or sealing between
the stencil and the board surface.
The problem with HASL, as Dr. Parker stated below, is that the round
bump (meniscus) of HASL sticking up above the surface of the pad on vias
and on surfaces where there is no accomodating hole in the stencil
prevents this tight seal, and allows the paste to squeeze out. (The
aperture design is typically slightly smaller than the pad). It is also
a problem when you go back and perform pick-n-place, as now you want to
place the SMT components onto your perfectly formed bricks of paste, but
with about 50-100 grams of pressure. If the paste is not stable to a
flat pad, the parts slide all over the place. While some of this is
forgiven by the surface tension of the solder in liquidus, bridges do
form, components misalign, etc. This is especially critical in a
no-clean process. If large (relatively) amounts of the solder paste are
not "tight to the brick" and fully registered on the pad, the paste does
not fully agglomerate into a single solder joint. Separated solder paste
does not usually conglomerate back into the central solder joint during
reflow. Extraneous solder balls form. This is very bad news if you did
not plan on washing them away.
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Lee parker
Sent: Tuesday, October 11, 2005 12:03 PM
To: [log in to unmask]<mailto:[log in to unmask]>
Subject: Re: [TN] Hasl
Ramon
After reflowing a soldered surface, you will form a meniscus which will
interfere with SMT component placement. To avoid the problem I suggest a
flat metal finish such as immersion silver or flash gold (not ENIG)
Best regards
Lee
J. Lee Parker, Ph.D.
JLP Consultants LLC
804 779 3389
----- Original Message -----
From: Dehoyos, Ramon<mailto:[log in to unmask]<mailto:[log in to unmask]>>
To: [log in to unmask]<mailto:[log in to unmask]<mailto:[log in to unmask]<mailto:[log in to unmask]>>
Sent: Tuesday, October 11, 2005 12:52 PM
Subject: [TN] Hasl
Hi technetters:
Is there a fine pitch limit to the use of HASL board
plating
finish due to its variation in thickness? Does selective solder strip
and reflow plating, SSSR, have a significant advantage over HASL? Any
comments relating to platting finish would be greatly appreciated. I
thank you for your comments.
Ramon
ME
410.552.2210
---------------------------------------------------
Technet Mail List provided as a service by IPC using LISTSERV 1.8e
To unsubscribe, send a message to
[log in to unmask]<mailto:[log in to unmask]<mailto:[log in to unmask]<mailto:[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]<mailto:[log in to unmask]<mailto:[log in to unmask]<mailto:[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]<mailto:[log in to unmask]<mailto:[log in to unmask]<mailto:[log in to unmask]>>: SET Technet Digest
Search the archives of previous posts at:
http://listserv.ipc.org/archives<http://listserv.ipc.org/archives<http://listserv.ipc.org/archives<http://listserv.ipc.org/archives>>
Please visit IPC web site
http://www.ipc.org/contentpage.asp?Pageid=4.3.16<http://www.ipc.org/cont<http://www.ipc.org/contentpage.asp?Pageid=4.3.16<http://www.ipc.org/cont>
entpage.asp?Pageid=4.3.16> for additional information, or contact Keach
Sasamori at [log in to unmask]<mailto:[log in to unmask]<mailto:[log in to unmask]<mailto:[log in to unmask]>> or 847-615-7100
ext.2815
-----------------------------------------------------
---------------------------------------------------
Technet Mail List provided as a service by IPC using LISTSERV 1.8e To
unsubscribe, send a message to [log in to unmask]<mailto:[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]<mailto:[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]<mailto:[log in to unmask]>: SET Technet Digest Search the
archives of previous posts at: http://listserv.ipc.org/archives<http://listserv.ipc.org/archives> Please
visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16<http://www.ipc.org/contentpage.asp?Pageid=4.3.16> for
additional information, or contact Keach Sasamori at [log in to unmask]<mailto:[log in to unmask]> or
847-615-7100 ext.2815
-----------------------------------------------------
---------------------------------------------------
Technet Mail List provided as a service by IPC using LISTSERV 1.8e To
unsubscribe, send a message to [log in to unmask]<mailto:[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]<mailto:[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]<mailto:[log in to unmask]>: SET Technet Digest Search the
archives of previous posts at: http://listserv.ipc.org/archives<http://listserv.ipc.org/archives> Please
visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16<http://www.ipc.org/contentpage.asp?Pageid=4.3.16> for
additional information, or contact Keach Sasamori at [log in to unmask]<mailto:[log in to unmask]> or
847-615-7100 ext.2815
-----------------------------------------------------
---------------------------------------------------
Technet Mail List provided as a service by IPC using LISTSERV 1.8e
To unsubscribe, send a message to [log in to unmask]<mailto:[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]<mailto:[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]<mailto:[log in to unmask]>: SET Technet Digest
Search the archives of previous posts at: http://listserv.ipc.org/archives<http://listserv.ipc.org/archives>
Please visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16<http://www.ipc.org/contentpage.asp?Pageid=4.3.16> for additional information, or contact Keach Sasamori at [log in to unmask]<mailto:[log in to unmask]> or 847-615-7100 ext.2815
-----------------------------------------------------
---------------------------------------------------
Technet Mail List provided as a service by IPC using LISTSERV 1.8e
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
-----------------------------------------------------
|
