I think that the material slash sheet are good general indicators but
also provide challenges in selecting a good material. Werner's STII
method helps focus the materials selection process.
Sincerely,
Paul Reid
Program Coordinator
PWB Interconnect Solutions Inc.
235 Stafford Rd., West, Unit 103
Nepean, Ontario
Canada, K2H 9C1
613 596 4244 ext. 229
Skype paul_reid_pwb
[log in to unmask] <mailto:[log in to unmask]>
________________________________
From: Jack Olson [mailto:[log in to unmask]]
Sent: May 21, 2010 11:29 AM
To: Paul Reid
Cc: TechNet E-Mail Forum
Subject: Re: [TN] My first RoHS circuit board!
That seems like very good advice, thanks for sharing it.
I'm happy to report that my crisis of confidence has passed.
Several people wrote to me to say that the materials my supplier
suggested (S1000-2 and IT-180) are rated for /126 and /129, even though
the data sheets I was given say /99 and /24.
I now have newer data sheets for both materials, and they do say /126
and /129 on them
I feel like a goofball getting everyone involved when I could have
looked it up myself, but I never would have suspected my supplier's data
sheets could be out of date!
thanks,
Jack
.
On Fri, May 21, 2010 at 9:30 AM, Paul Reid <[log in to unmask]>
wrote:
Hi Jack,
Our experience has been that it is not a good idea to ask a fabricator
to use a material with which they have no experience unless they are
willing to test the material and make various process changes to
maximize the PWBs robustness. If you force a material on a fabricator
then you own the results, good or bad. If the fabricator suggests a
material then they can be held accountable for the results.
We have seen dicey cured material that tested reliable for lead free
assembly in low layer count, low aspect ratio PWBs. The default lead
free, FR4 material, however, is phenolic cured because in general
phenolic cure materials are usually more robust in HDI, RoHS compliant
applications.
I know, and I believe Werner and Dewey would agree, that some high Tg
materials offer no reliability advantage over lower Tg materials. Tg
should be considered an indicator but not a definer of overall material
robustness. I am beginning to think elasticity and the ability to
maintain elasticity after the thermal excursions associated with lead
free assembly and rework may be just as important as Tg and Td.
In challenging applications fabrication, material, design and
construction all need to be maximized is order to achieve acceptable
reliability.
All that being said we promote reliability testing of representative
coupons to determine which materials are best suited for an application
particularly with challenging designs and high reliability expectations.
Sincerely,
Paul Reid
Program Coordinator
PWB Interconnect Solutions Inc.
235 Stafford Rd., West, Unit 103
Nepean, Ontario
Canada, K2H 9C1
613 596 4244 ext. 229
Skype paul_reid_pwb
[log in to unmask] <mailto:[log in to unmask]>
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Jack Olson
Sent: May 20, 2010 9:03 PM
To: [log in to unmask]
Subject: Re: [TN] My first RoHS circuit board!
Thanks for the advice (everyone!)
Here's an update if anyone is interested:
I sent a sample fab dwg to our primary supplier (in China) with notes
that incorporated several of your recommendations (the main one being
material /126 170Tg 330Td 30minT288) to see if it would cause them any
problems before I send them the real order. They looked at it and said
"No
Problem. Our default material meets those requirements"
So I told them that since I'm trying to learn about his I would like to
know
what kind of material it was, and could they send me a data sheet.
Well, they sent a data sheet for something called S1000-2 which it says
right on the data sheet is /99, but the parameters are 175Tg 335Td
10minT288
So I wrote back and asked if they had another material that is more
robust,
and they sent me data for a material called IT-180 which it says is /24
Tg180 Td350 >60minT288(?)
I really don't think they are trying to be deceptive, but that they
honestly
think the only thing that matters is the Tg and Td numbers. And those
numbers look pretty good!
So now I'm wondering how hard I should push to get them to literally buy
/126, and if by forcing them to use a material they aren't familiar
with, if
there will be other problems related to drilling, or desmear or plating
or
routing or whatever could be different from the /99 they are used to. Is
there a "learning curve" with these materials?
Jack
.
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