Bob,
I read through your email and noticed a few things that have me asking
additional questions. First, what industry do you work in and is RoHS
compliance a requirement for this industry? Second, you stated that the
components in this design will be a mixture of tin-lead and lead-free.
Did you know you can not mix tin-lead components in a lead-free assembly
environment? You can however mix some lead free components (obviously
not BGA's) with a tin-lead assembly process.
ENIG, electroless nickel immersion gold, is a finish among others (such
as immersion silver) that can be used in a lead-free process. If you
want you can use ENIG with a tin-lead assembly process. People do this
all of the time when looking for co-planarity for use with BGA's. Which
brings up the next topic of concern, did you say you were using HASL
with BGA assembly? What pitch BGA's are you using? Must not be fine
pitch.
Lastly, you are looking for a high temp material (high Tg) to use with a
lead-free assembly process. What you really need to look for is a
material with a high thermal degradation (high Td) not necessarily a
high Tg. One suggestion for a high Td material suitable for lead-free
assembly processing is Isola's IS410 or IS420. Nevertheless, there are
several other material manufactures that offer these types of materials
such as Park Nelco, Polyclad and others. Your best bet is to look for a
material that fits your thermal, electrical and assembly processing
requirements by reviewing these companies material datasheets.
Maybe you really have a requirement for RoHS and you want to start
getting things ready for compliance. You can start by changing the PCB
material, the PCB finish and start buying lead-free parts but you can
not run this assembly through the lead-free assembly process until all
of the parts on the BOM are lead-free. Care will need to be taken to
track the tin-lead and lead-free components so that you know which parts
can or can not go through the lead-free assembly processes.
Additionally, parts like BGA's which might now have lead-free (SAC)
solder balls can not go through the tin-lead process because the solder
balls need to reflow at a high temperature. RoHS compliance is very
complicated to implement and track properly.
I hope you find this small bit of information useful. There is a
lead-free forum that you should probably sign-up for.
Thanks
Tony Cosentino
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-----Original Message-----
From: DesignerCouncil [mailto:[log in to unmask]] On Behalf Of
Robert Walker
Sent: Wednesday, January 18, 2006 12:39 PM
To: [log in to unmask]
Subject: [DC] RoHS board finish
Hi All,
I'm doing my first PCB design that will use lead-free components and I
need to change my board finish from what I've always used.....HASL. I'm
looking for any recommendations or comments on the best board finish to
use.
The components used on the design will be a mixture of tin-lead and
lead-free (SAC), so I'm not sure if there is a preferred finish to use
in this type of situation. I work in a prototype environment where the
boards may be reworked (BGA removal/replaced) a number of times, so I'm
concerned about the ability of the finish being able to handle being
reworked/reflowed a number of times.
I'd also welcome any recommendations on the type of board material to
use since it will see an elevated temperature of up to 260C. I've always
just specified FR4 in the past.
Thanx in advance for any feedback.
Regards,
Bob Walker
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