Hi membranos (spanish: member brains),
have got splendid help from many of you about soldering superBGAs on FR4
etc. Squirreling this theme I got advices in dark corner of the clubrooms,
guru X,Y and Z whispered: 'don't use concoat that zips under sBGAs, will
pump your  balls loose in less time than it takes to...now, can't tell u
more, yo warned'. So I was lured to dig in this jungle too. With my machete
I found some paths that led to TCE for some concoats, among which we use
Humiseal 1B31 with TCE=55 ppm/K. Others:

----------------------------------------------------------------------------
----------------------------------------------------------------------------
---------
                        -100C           -55C            +20C            +100
150C            +200C

Conathane EN11  66              66              120             229
229             ----

Solithane 113           87              87              transition      212
softening       n/a

Uralane 5750LV          120             120             172             270
270             n/a

CV-1144 ----------  ----------  too soft for measuring TCE
-------------------------------------------------------------------

Mapsil 213              576             245             310             263
145             n/a

Sylgard 184             696             804             309             205
278             n/a

Scotchcast 280          78              78              78              213
207             n/a

----------------------------------------------------------------------------
----------------------------------------------------------------------------
--------

Glass epoxy G10 13              13              13              13
13              13
XY-direction

Glass epoxy G10 39              39              39              50
340             340
Z-direction

----------------------------------------------------------------------------
----------------------------------------------------------------------------
-----------

Now, looking on this table (by Matra/Marconi, praised be their good reports)
you wonder what is matching and not in this world. Our concoat unhappily is
sucked in under the sBGAs and during heat and cold there will be a
struggling and puffing and mourning in this structure. Notice this:

Humiseal say TCE same 55 ppm/K over whole range -65 to +125C while some
above behave very different at extreme cold and heat, as you can see. I have
to trust Humiseal, but strange it is. So I go for TCE 55 ppm/K.

Then what about the FR4 boards big diff between XY and Z TCE? With Humiseal
TCE=55 ppm/K you get a neat  match in XY, as it seems:  13 vs 55. But what
in Z-direction? 39 vs 55 is OK but the board behaves really bad beyond
+100C. You have 340 vs 55, that does not look quite so good.

I hope that Graham N or someone will sweep the clouds away with his fairy's
magic stick and tell me if the darkmen above are right or not.

To glue or not to glue, that's the adhesion

Ingemar  Hernefjord
Ericsson Microwave Systems

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