Hi Bev, and FL-RaoulC, IPC LF Listservers,

Thanks for coming to my and our rescue.

I knew as soon as I hit the send key, I goofed up on TGA and TMA, so that
is why I quickly sent the 2nd note on DSC without a proper web reference.
I know I know, I was Brain Dead on my first note. It is my recollection
that after pulverization DSC is the std and cheap technique used to obtain
Gross Pb percentages. DSC I believe is used in Geology work.

Thanks for describing how difficult it is to prepare the samples for High
Energy analysis. From your description it does seem like a good analyzer
has to prepare samples in different ways to obtain some bounds on the
percentages. I would hope now days the preparation wouldn't add more
than 2-3% to the uncertainty.

YiEngr, MA/NY DDave  Dave


David,
TGA, TMA and DSC are NOT the tools to use for finding out how much lead is
in a circuit board.  TGA and TMA will not even tell you whether lead is
present.  Thermal gravimetric analysis is a technique for examining weight
loss with temperature change, usually temperature increases.  Even if you
have one that can go to high enough temperatures to completely ash a sample
of a circuit board, you would still be left with the tin, copper, gold,
nickel and the borosilicates from the glass fibers.  Note I said sample,
because you can only put in a very small piece and it will not be
representative of your whole board.  TMA stands for thermal mechanical
analysis.  I cannot imagine how you think this is going to help you find
lead in a quantitative fashion.  DSC or differential scanning calorimetry
measures heat transfers.  So one can find melting points, but unless you
had pure lead, how would you know that lead was present?

If you really want to know how much lead is on a circuit board you either
have to have data from your board supplier (if it is a HASL board) and all
your component suppliers and measure a bare board with and without solder
paste and then do some calculations OR you take circuit packs, grind them
up and have them analyzed by a very good lab with an atomic absorption
spectrometer or an emission spectrometer.  This is not as easy as it sounds
because then there are questions like: how fine do I grind it, how long do
I leave it in the dissolving medium,  how do I get everything in solution,
what is dissolved as opposed to colloidal, are there interferences in the
analysis, how long can I leave my samples between dissolution and analysis
before there is terminal precipitation, etc.?  This is going to be one very
expensive nightmare before it is all over.
sincerely,
Bev Christian
Research in Motion

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