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Re: Space Grade Soldering ?



Tim

> I've been reading about the construction of a few microsats 
> and I see "Space Grade Soldering" mentioned a few times. So 
> I'm curious as to what that entails ?

This is a question where you'll ask three different engineers the same
question and you'll likely get three different answers.

I can't comment on the Microsats specifically, but in my experience at ESA
there are a whole bunch of things we have adhered to in the past.

Firstly, 60/40 is good. Anything RoHS is bad. This is predominently due to
'tin whiskers' that the lead in the solder significantly resists. This leads
to early failure in devices as the tin whiskers grow and short out
previously insulated conductors.

I am not sure of the specific flux they use in the solder.

I am aware that reflow is often suggested as a way of soldering that
prevents cracking of components by uniformly heating the whole device. This
isn't universal practice though. Again this is to reduce early failure of
devices due to weaknesses from stressing the part during conventional
soldering.

We also use special anti-wicking pliers when soldering interconnecting wires
(PTFE) to PCBs: that stops the solder running down into the wire behind the
PTFE insulation. Then a small loop is made and the wire is glued a few mm
(length dependend on the wire gauge) from the solder pad. This procedure is
to provide a uniformly strong bond without weaknesses when it goes to the
shake tests.

Generally PCBs have no coatings at all prior to mounting the components: no
silk screen or resist. This is to reduce the chances of outgassing from
small bubbles that may have formed during fabrication.

After the components have been mounted and the poulated PCB is tested,
conformal coating is used, which is basically a guy with a tin of goo and a
brush. The goo is generously brushed over the all the components and the
entire pcb. Once hardened, it is designed to prevent outgassing and provide
some resistance to vibration shock.

All this is done in a clean room, wearing disposable gloves and protective
clothing to try to stop any foreign object damage including grease and other
body gunge attaching itself to the parts.

73, Howard G6LVB

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