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September 1999

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Wed, 22 Sep 1999 15:28:26 +0800
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Hi Sherry,

Yr input pertaining HASL is a valuable info. For me.

I do hope you could share with me:

1)      Why there is the solder ball exist in via hole in HASL process?
2)      How to eliminate the solder ball issue?

Regards,
OH Yeoh

                -----Original Message-----
                From:   Sherry Goodell [mailto:[log in to unmask]]
                Sent:   Wednesday, September 22, 1999 10:51 AM
                To:     [log in to unmask]
                Subject:        Re: [TN] HASL...

                Ron and Steve,

                These really are excellent questions.  I will attempt to
address them.  Here
                it goes.

                First, to answer your question, Steve, there is no
documentation that I am
                aware of stating the limitations of HAL by feature size.
There are a lot of
                perceptions and opinions, but nothing formally documented.

                The closest thing to a statement on HAL capability that I am
aware of is a
                document called Specification Guidelines, rev. 5A, which is
downloadable at
                www.tet-halco.com or www.huggroup.com .  This was put out be
Teledyne due to
                the fact that there was nothing documented and the intent
was to try and
                establish some kind of guideline on HAL capability.

                Ron, yours are bit more complicated.  I will attempt to
answer each and hope
                to get some comments back.
                1. What is the finest pitch that can be used with the HASL
process?????

                First, not all HAL is equal. My recent experience is with
horizontal HAL and
                that is what I will address here. I am not current on all
the vertical
                equipment and quality that they can deliver so any vertical
capabilities I
                could quote would unfair.

                With Horizontal HAL, depending on the solder thickness' you
are looking for,
                you can process down to 5 mil lines and spacing without
bridging.

                QFP features less than 20-mil pitch requires a skilled
operator and precise
                controls to be in place.  They also require that the panel
be processed at a
                full 45-degree angle and minimal variation from this
critical to the
                uniformity of the solder thickness.  Pitches of 20-mil and
greater are
                processed in many shops on a regular basis and with
horizontal HAL. They
                typically run around a 300 microinch mean with a standard
deviation of
                around 50-60 microinches.  That provides a +/-3 sigma
capability within the
                typical 100-1000 microinch specifications.  Please reference
the
                Specification guidelines for information on these
capabilities.

                2. Does the HASL process still produce the doming affect on
traces and
                pads???
                Question:  If the HASL process, now days, can produce a
relatively flat
                surface, then, with solder paste screened onto the CCA the
parts should stay
                in place.  "In place", meaning not skewing from one
direction or the other.


                This is a loaded question. Solder by its nature, forms a
"crest".  This is
                not new.  When you speak of the 'doming affect' are you
referring to uneven
                deposits and/or distribution?  I assume you are concerned
about the QFP
                sites? Again, with horizontal HAL, provided the panels are
processed at
                proper angles, the QFP sites should be uniform and
"relatively" flat over
                the length of the pad.  They will however, have solder
crests at the center
                of the width.  This condition, to the best of my knowledge
has not
                contributed to component skewing.  In most cases, there is
paste on the pad
                and the minor cresting is not an issue.

                The bigger problem is the coplanarity or uniformity of the
pads.  The
                information I have been getting lately indicates that most
assembly
                processes do not see a problem as long as there is no more
than
                650-microinches variation within a feature group.  Again, if
the panels are
                processed at the proper angle, there is no problem meeting
this requirement.
                There is another paper called "The Benefits of Angle" I
could get you a copy
                of this off line if you are interested.  This explains why
the 45-degree
                angle is so important to the process.

                In 15 years of providing horizontal HAL coating in a solder
service, I have
                not had a single return or complaint for solderability or
component skewing.


                3. If fiducials are a problem for vision equipment, then
what steps can be
                taken to keep fiducials level for the vision equipment?????

                Are fiducials still a problem for vision equipment?

                I have not heard of this problem in some time.  I know that
this was an
                issue some time ago and there was a rough learning curve,
but with much
                improved results, to the best of my knowledge, this has been
resolved.  If
                anyone is still having this problem or found a way to
correct it, please
                share it with us.

                4. Next question is concerning mounting holes and ground
planes.  Will HASL
                leveling give as good a ground plane as Ni/Au??????

                Can you define what you consider "good" for a ground plane?
HAL will leave
                a thin coating of solder over a ground plane.  Ground planes
are not
                typically soldered to that I know of, so I am not sure what
the question is.

                Mounting Holes?  If they are plated through, one side will
have a slightly
                heavier deposit on the pad than the other, but I am not
aware of any
                problems.  If they are non-plated through and your concern
is location, with
                the horizontal process having a very short, 2-3 second,
uniform dwell time,
                and being held flat, there is minimal movement and/or
warping seen.  Again I
                am not aware of any issues with this.

                5.  What about BGA technology????   Does this question roll
up into question
                number one????

                        BGA results have been very good with HAL and because
they are round they do
                have the same requirement for the critical 45-degree angle
at processing.

                HAL serves as a good inspection tool prior to assembly.  If
there is a
                contamination problem on the board, you will know it well
before wave
                solder.  Since the IMC is formed at HAL, the surface will be
de-wetted and
                can be seen long before you load expensive components to the
board. Properly
                taken XRF thickness data will tell you if you will have any
skewing issues,
                and solder won't contaminate your wave machine.

                There are many perceptions that HAL is not a capable
process.  It is clearly
                not for every application.  Wire bonding for example does
not lend itself to
                HAL. It is, however, much more capable than often given
credit.  There is a
                HAL User Group called HUG , which is relatively new, but in
a short time,
                extensive data collection and testing has been undertaken to
define and
                better understand the capabilities and limitations of HAL.
There are
                solderability, IMC and assembly testing currently in
progress.  Anyone
                interesting more information on the group can contact me
off-line or go to
                www.huggroup.com

                I hope this is of some help.  Please let me know how you
make out.

                Sherry Goodell
                Mgr. Applications Eng, TET Halco
                phone: 603-427-8653
                Fax: 603-434-4156
                e-mail: [log in to unmask] or [log in to unmask]
                > -----Original Message-----
                > From: TechNet [mailto:[log in to unmask]]On Behalf Of
Hollandsworth, Ron
                > Sent: Monday, September 20, 1999 12:24 PM
                > To: [log in to unmask]
                > Subject: Re: [TN] HASL...
                > Importance: Low
                >
                >
                > Steve:
                > Excellent question, and the timing is perfect.
                >
                > 1.  What is the finest pitch that can be used with the
HASL process?????
                >
                > 2.  Does the HASL process still produce the doming affect
on traces and
                > pads???
                >         Question:  If the HASL process, now days, can
produce a relatively
                > flat surface, then, with solder paste screened onto the
CCA the
                > parts should
                > stay in         place.  "In place", meaning not skewing
from one direction
                > or the other.
                >
                > 3.  If fiducials are a problem for vision equipment, the
what steps can be
                > taken to keep fiducials level for the vision
equipment?????
                >
                > 4.  Next question is concerning mounting holes and ground
planes.
                >  Will HASL
                > leveling give as good a ground plane as Ni/Au??????
                >
                > 5.  What about BGA technology????   Does this question
roll up
                > into question
                > number one????
                >
                > The reason for my questions is because of the Ni/Au
contamination
                > issues.  I
                > thought that the problem was more prevalent with boards
                > associated with only
                > wavesoldering, however, I have learned today that SMT is
not immuned.  I
                > have had many of one type of board that has been assembled
through our
                > process without incident.  Then, all of a sudden, we have
the
                > contamination
                > issue.  When checking our process, we see no process
change.  It comes, it
                > goes, and in the mean time it is very expensive when
circuit card
                > assemblies, not bare boards, have to be scrapped.
                >
                > Ron Hollandsworth
                >
                >
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