We are using Immersion Tin. It is comparable to Iag and at most
vendors Tin is cheaper than Gold.
Joe J.
-----Original Message-----
From: DesignerCouncil [mailto:[log in to unmask]] On Behalf Of
Susan C. James
Sent: Thursday, January 19, 2006 10:36 AM
To: [log in to unmask]
Subject: Re: [DC] RoHS board finish
Bob and Jack,
We're using IAg finish. Some out there will disagree, but we see
potential problems with the other finishes that we want to avoid.
That's not to say IAg is perfect. I suspect that lead-free HASL may
take a stronger foothold someday, but for now it seems that there are
not a lot of suppliers offering it. But with BGAs you probably won't
want to use any kind of HASL (we don't use them here).
Laminate choice is key to a successful lead-free program. We spec
laminate and prepreg per IPC-4101B/99 (not yet released [I think]) with
a specific requirement of 170 degrees C min. Tg. I send a copy of the
/99 sheet with the fab drawing. It's been argued that the slash sheets
don't provide the best selection criteria, but it's a very good place to
start.
Here are some key points from a white paper I wrote for my company. Of
course, this info will be dependant upon your product and assembly
requirements, along with product environment and life cycle issues.
<snips>
PCB reliability factors include the ability to withstand environmental
and thermal stresses. Field performance is affected by the laminate,
hole wall and interconnect strength, surface finish, assembly and rework
processes.
An important question to consider is what life will be left after the
rigors of assembly and rework.
Major decision making elements:
Thermal performance of the resin system
Decomposition temperature (Td)
Coefficient of thermal expansion (CTE)
Glass transition temperature (Tg)
Continuous operating temperature
Curing agent
Environmental properties
Moisture absorption rate
CAF resistance
Flame retardant mechanism
Electrical properties
Storage, shelf life, handling
<end snips>
Also remember that the time board materials see at temperature is
cumulative. This is one reason why some are over-spec'ing their
laminates, along with the fact that there's just a lot of unknowns. Not
a lot of empirical data out there but more is accumulating.
Sign up for the TechNet and LeadFree forums. There are experts there
who share info and give good advice. Hope this helps.
Regards,
Sue James
Taylor Company
815-624-5444
-------Original Message-----
Date: Wed, 18 Jan 2006 12:39:06 EST
From: Robert Walker <[log in to unmask]>
Subject: 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
[log in to unmask] (mailto:[log in to unmask])
-------Original Message-------
Date: Wed, 18 Jan 2006 13:08:33 -0600
From: "Jack C. Olson" <[log in to unmask]>
Subject: Re: RoHS board finish
If you don't want to switch vendors, you might ask them what they
are
capable of (instead of sending out to a third party) and what they
have the
most experience using.
Personally, we have had great success with Immersion Silver, and
it
doesn't
increase the cost of the board like ENIG does.
I hope soemone else answers you about the MATERIAL, because I want
to
know!
Jack
(630) 754-2431
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