Hi Werner, thanks for the reply. I will try to be brief; see below. Rgds, 
Valerie



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05/22/2006 01:34 PM

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Re: [TN] Rohs Weeeeeee board material

Hi Valerie,
You are giving me a rather lengthy response?so I will go point by point.
1)
The Isola site is also used to track order and ship status, invoicing, and
dock to stock in addition to technical details; so it would be entirely
appropriate that they do not just approve all comers but first understand
who is requesting access to what - so they are asking for 24 hours to
review the registration 
A: If it works like that, it would be acceptable, BUT 5 days after asking 
for registration, i still have not heard from them. And why restrict 
access to technical data.
Valerie: Ok; I'll see how long it takes for them to get back to me and let 
you know. They state 24 hours; and if it turns into 5+ days, I agree that 
is excessive. Nelco also wants you to register to get to their tech 
files....

2)
When I only see DSC, I subtract 10 degrees and call that value the
equivalent to the Tg by TMA - and move on. 
A: I do the same.

3)
Since the IPC has test methods for all three tests, they are all valid. 
A:  I think the IPC is doing a lot for the industry, BUT I would not go as 
far as you and say "Since the IPC has test methods for all three tests, 
they are all valid."
Valerie: I mean valid in the sense of a "defined" test used to determine a 
property, as opposed to some test someone made up. However having 3 tests 
to define the same property is a problem. On the other hand, IPC does 
describe the probable result deltas between the tests.

4)
Interestingly, IPC 4101 does not require any Tg testing. For Tg it states 
that those are "optional tests as agreed upon between user and supplier", 
and they reference both TMA and DSC as "the tests" for Tg.
A:  That is one of the reasons that I have voted 'Negative' on the 4101 B 
revision. The prime reason is the wide ranges of properties allowed on 
each slash sheet. The problem is, that too many vendors in the committee 
have too mch vested interest. We need to think more in terms oof 'Win-Win' 
scenarios. 
Valerie: At this point in time what little respect I had for the slash 
sheets is totally gone. As far as I am concerned they are useful only in 
the most general sense to differentiate one "family" of materials from 
another; ie: polyimide vs epoxy or fiberglass reinforced vs aramid fibers, 
and all the other permutations. Which means effectively that the only 
portion of the slash sheet that has any value is the "description fields" 
above the solid lines. Ok, maybe I exaggerate a little.. and I did go on 
for a bit on this topic. If anyone thinks that specifying a slash sheet 
means that they have "quality" material or "suitable" material, they are 
mistaken. All they have done is describe the generic resin and 
reinforcement; after that, it means almost nothing with regard to 
performance and use.

5)
x,y-TE is below Tg, so it is low. Almost all FR4s with woven glass are
somewhere between 10 and 14; and that number would also change in practice
when one moves from a raw laminate core to a cured multilayer board. 
A:  Well, those numbers do not make sense--where do 10 to 14 come from. I 
have never seen values this low-they typically are 16+/-2 ppm/C. When I 
had one of these materials measured, the values turned out to be 
CTE(x,<Tg)=21.4 and CTE(y,<Tg)=16.0. Can you imagine the incorrect Design 
for Reliability for the SMT solder joints based on CTE's of 11 and 13?
Valerie: This answer will have to go on a little bit: to get equivalent 
results you would need to be measuring the same thickness material, with 
the same glass style, with the same percentage resin. The TM 2.4.41 states 
that the test specimen shall be between 0.05 and 0.30 inches !! Further, 
it may be as received material or it may be laminated from b-stage. For 
the test, the upper temperature is "the temperature of interest", and I 
think we would both agree that it matters what that temperature is. Also, 
the population is three specimens from the same piece of material for each 
direction.... 
Poly 370Hr is 14,16; IS 408 is 13,13; IS410 is 11,13; MEM R1755 is 10,14; 
Nelco 4000-11 is 12,14 .... The value of 16 +/-2 ppm/C is what we use for 
multilayers which combine epoxy, fiberglass and copper into a composite 
CTE; copper being usually quoted as 17 ppm/C.
I agree that using 11 or 13 or something as input into a formula to 
determine Design for Reliability with certain device packages would be a 
problem. Which is why nobody pays much attention to it anyway and uses 16 
or 17 (anyone I have talked to about this, at any rate).

6)
In general I would say that USA laminators didn't pick up on the
enormity of the research and development that it would take for RoHS
capable materials; ie: able to withstand lead-free process temperatures.
A:  AMEN, to that. I am already seeing the consequences.
Valerie: Yes, I'm sure you are; and it is not a pretty picture.


Werner

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