Thanks folks for all your great input, but I'm still without a clear
understanding of the IMC subject and may never be.

It is not hard for me to get confused at my advanced age and congenital
ignorance. I?m just not getting a consistent picture. Could someone paint it
for me ? for us all. First, the following is what I think I know:

1) I should have said non-surface scientists (me especially) look at a
surface as what it is apparent as an objects area having no depth.

2) Surface scientists clearly understand surface as definitely having depth
down to the surface?s beginning (about 1,000 angstroms or so) and understand
that atomic layers (not mono-layers ? very poorly put) comprise this ?depth
to surface.?

3) Soldering is defined as the joining of two metal surfaces, with a solder
medium (eutectic most commonly composed of tin-lead but changing to
something lead free soon) requiring both diffusion and intermetallic
formation (not Manko?s original definition) at temperatures below 800 F.

4) I know all processes are capable of being mis-managed including HASL. I
just find it more difficult to manage effectively across so many suppliers.
I'll not go farther with this. Each of us has to make a decision concerning
a process and its effects.

5) I recognize that rework cycles, be they two or three, have more impact on
circuit integrity as pad bond strength, etc. I still need to know how much
is too much concerning intermetallic growth and its correlation to solder
joint reliability.

What follows is what?s confusing to me:

1) I THINK Werner says thick IMC formations are essential and good for
reliable solder joints. Is this right?

2) Aside from board/pad damage, can there be too many soldering operations
performed

3) Is there a maximum or minimum IMC thickness to assure reliable solder joints

4) Does Phil agree about IMC thickness

5) Does Peter Duncan agree about IMC thickness

6) Do Manko and Rahn agree

7) Is this what Wassink says and knows and is it converse to all the above
except Werner

The main reason I?m asking is to gain objective evidence concerning eutectic
lead soldering techniques having been around since before the time of
Christ. Then, I would like to apply some of this understanding to what
concerns us all as lead free soldering using who knows what. So, this means,
I?m really no longer interested in stirring the pot, nor am I interested in
becoming an expert. I just want a handle on this stuff as there still seems
to be too much opinion.

I just want to learn more about what I once thought I knew a little
something about.

Earl Moon

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