Hello,
I am glsd you found the information useful.
By a solder ball in the via hole, I think you mean a solder deposit in the
hole, that takes the shape of a ball and is frequently raised above the
surface of the panel? This condition is typical when you have a partially
filled via hole at HAL. Solder fills the cavity, and the air tries to blow
it out, but it cannot because there is soldermask blocking the hole. This
forms what we call a coke bottle effect and the air becomes turbulent. The
solder that is not removed, forms a natural ball shape as the surface
tension of the solder pulls the solder to itself.
The way to overcome this is for the fabricator and end user to work together
and allow the via holes to be open at HAL. They can be plugged after HAL if
need be.
> -----Original Message-----
> From: [log in to unmask] [mailto:[log in to unmask]]
> Sent: Wednesday, September 22, 1999 3:28 AM
> To: [log in to unmask]
> Cc: [log in to unmask]
> Subject: RE: [TN] HASL...
>
>
> 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
> >
> >
> ##############################################################
> > TechNet Mail List provided as a free service by IPC using
> LISTSERV 1.8c
> >
> ##############################################################
> > To subscribe/unsubscribe, send a message to
> [log in to unmask] with
> > following text in
> > the body:
> > To subscribe: SUBSCRIBE TECHNET <your full name>
> > To unsubscribe: SIGNOFF TECHNET
> >
> ##############################################################
> > Please visit IPC web site
> (http://www.ipc.org/html/forum.htm) for
> > additional
> > information.
> > If you need assistance - contact Gayatri Sardeshpande at
> [log in to unmask] or
> > 847-509-9700 ext.5365
> >
> ##############################################################
> >
>
>
> ##############################################################
> TechNet Mail List provided as a free service by IPC using
> LISTSERV 1.8c
>
> ##############################################################
> To subscribe/unsubscribe, send a message to [log in to unmask]
> with following text in
> the body:
> To subscribe: SUBSCRIBE TECHNET <your full name>
> To unsubscribe: SIGNOFF TECHNET
>
> ##############################################################
> Please visit IPC web site
> (http://www.ipc.org/html/forum.htm) for additional
> information.
> If you need assistance - contact Gayatri Sardeshpande at
> [log in to unmask] or
> 847-509-9700 ext.5365
>
> ##############################################################
>
##############################################################
TechNet Mail List provided as a free service by IPC using LISTSERV 1.8c
##############################################################
To subscribe/unsubscribe, send a message to [log in to unmask] with following text in
the body:
To subscribe: SUBSCRIBE TECHNET <your full name>
To unsubscribe: SIGNOFF TECHNET
##############################################################
Please visit IPC web site (http://www.ipc.org/html/forum.htm) for additional
information.
If you need assistance - contact Gayatri Sardeshpande at [log in to unmask] or
847-509-9700 ext.5365
##############################################################
|
