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Subject:	Specifying Base Materials
From:	Jack Olson <[log in to unmask]>
Reply To:	(Designers Council Forum)
Date:	Mon, 29 Oct 2007 12:55:28 -0500
Content-Type:	text/plain
Parts/Attachments:	text/plain (54 lines)

I was asking a question about base materials over on TechNet, and stumbled
over a thought that I can't answer

Quite often (like EVERY presentation) we are being told to specify better
materials if we have to do Lead Free soldering, right?

Here is a sample note:

MATERIAL: LAMINATE FLAME RETARDANT EPOXY-GLASS PER IPC-4101

/126, 170 DEGREE C MINIMUM Tg, AS TESTED PER IPC-TM-650,

2.4.24C (TMA METHOD). DECOMPOSITION TEMPERATURE TO BE 340

DEGREES C MINIMUM, AS TESTED PER IPC-TM-650, 2.4.24.6.

A T288 DELAMINATION TIME OF 35 MINUTES MINIMUM, AS TESTED

PER IPC-TM-650, 2.4.24.1C.

A MAXIMUM THICKNESS EXPANSION OF 3% FROM 50 – 260 DEGREES C.

PREPREG MATERIALS PER /126 SHALL MEET THE SAME REQUIREMENTS.

INNER LAYER FOIL PER IPC-4562, TYPE E, GRADE 3, CLASS 2.

So my question is, if IPC-4101/126 is already rated at Tg170 minimum, Td340
minimum, etc.
then
Why do we have to repeat it in the note?
Isn't that redundant?

Just as an informal poll, if you are doing lead free assembly, are you USING
a note like the one above?

Also, this isn't a base material question, but What is your minimum
acceptable hole wall thickness?
I've gotten advice that we should increase it, for better z-axis
reliability. Anyone doing that?
(I'm not questioning the wisdom of those numbers, just wondering if everyone
is USING them)

onward thru the fog,
Jack

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