Thanks Jeff. Is it from pad to pad or from thickest to thinnest
pad areas of the board? I would like to know if HASL plating creates a
planarity problem for QFPs or BGAs assembly for some people in the
industry.
Regards,
Ramon
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Jeffrey Bush
Sent: Wednesday, October 12, 2005 12:00 PM
To: [log in to unmask]
Subject: Re: [TN] Hasl
We control the thickness from .2 to .9 mils - pad centers. We use a
HSL-175 horizontal system.
Jeffrey Bush
Director, Quality Assurance and Technical Support
VERMONT CIRCUITS INCORPORATED
76 Technology Drive - POB 1890
Brattleboro, Vermont 05302
Voice: 802.257.4571.21 Fax: 802.257.0011
http://www.vtcircuits.com
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Dehoyos, Ramon
Sent: Wednesday, October 12, 2005 9:06 AM
To: [log in to unmask]
Subject: Re: [TN] Hasl
Thanks for your comments Dr Lee. I would like to know
from the fabricators what is the range in thickness that they can
control on a HASL plating finish. Is it 0.1 to 0.6 mills? From the
fabricators what is the finest part pitch that they can assemble on
PWBs.
Thanks for your inputs.
Ramon
ME
410.552.2210
_____
From: Lee parker [mailto:[log in to unmask]]
Sent: Tuesday, October 11, 2005 8:10 PM
To: TechNet E-Mail Forum; Dehoyos, Ramon
Subject: Re: [TN] Hasl
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]
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]
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]
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]>
To: [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
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