Homebrew PCBs

On Tue, 30 Mar 2004 16:34:14 -0000, ballendo <ballendo@...> wrote:

> Stefan,
>
> It seems you have had at least one bad experience at some point with
> traces coming off...
>
> With the older and/or cheaper bakelite type boards this can be a
> problem, but I sure haven't seen it with any of the glass-epoxy types.
>
> At any rate, if this is a concern, use of some epoxy which can adhere
> to the bare parts of the board between the traces will deal with it.
> And provide a conformal coating at the same time...
>
> Ballendo
>

You are right, i had bad experiences with traces coming off....

It happens more often with bakelite, i agree, but it does also happen with 
FR4.

In my opinion the glue that holds the copper is simply not made for taking 
any force,
especially if heating from soldering is involved. if you look at any 
professional board
(throughhole) you will see there is always some sort of spacer etc used on 
the top side
to counter the force. the pad (on a not plated through board) is never 
allowed to take
any force which would lift it off. the only parts where this is not true 
are transistors
sometimes.
With SMD this rule is greatly loosened, because you simply don't have the 
holes.
I guess you are right, and the glue holding the copper got better over 
time, along with the
smd developement so it can take more force. however i have not seen a 
substantial connector
in SMD with no mechanical restraint to prevent lifting of the pads.
The connectors i know which do not require any mounting holes have very 
low "pull out force"
of the plug. the ones with better sitting plugs have some sort of plastic 
"rivets" or are
at the edge of the board (Around it).

I had some bad experiences and do not want to repeat that.
Of course it will work (i also tack wires to the copper side for short 
tests etc.)
but i really think a good and long-term reliable board is designed to 
prevent such things.


The epoxy is certainly a good idea, there is another occasion where it is 
useful.
Sometimes you solder wires directly to a board, just like a resistor, with 
the isolation
on the top side, stripped through the hole.
If the wire is small gauge it will break if you move it too often.
Running the wire through another hole will remove the problem (a bigger 
hole and run
it through with the isolation on) epoxy helps if ther is no other hole or 
no space.

I have had several bad experiences with trace lifting, and wire breaking, 
too often.

ST


there is another thing, if you solder on the screw terminal like you 
described the
force is on the edge of the trace, having a very good lever. it is much 
more
likely to come off than if you pull on the center of a pad.