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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