Re: broken circuit board advice

On May 30, 11:22�am, Tim Wescott <t...@xxxxxxxxxxxxxxxx> wrote:
jped....@xxxxxxxxx wrote:
On May 29, 11:44 pm, m...@xxxxxxxxx wrote:
On May 29, 9:32 pm, jped....@xxxxxxxxx wrote:

So I have this little circuit board thing(don't ask what it is, I
don't really know myself, that's why I'm trying to fix it) that my
friend stepped on and broke the usb male end off of. �He said I could
have it if I could fix it. �Ok so anyway, I figured it would be a
simple matter of soldering the piece back on and that the solder
connections were the only things that were broken. �But, when i took a
better look at it, I discovered that the metallic area on the board
where the connections from the usb male end thing attached (as in
green part of the board and metallic part of the board) were broken
off. �I didn't even know that that could happen. �So, is there a way
to fix this? �I can't solder the connections back, because it won't
stick without those little metallic pieces. �Thanks in advance for the
help.
Have you scraped the solder mask?

I don't know what that means. �Sorry, I'm a noob. �If you mean, scrape
where the little metallic part used to be, then yes.

Circuit board anatomy:

The part that looks like a little board or card is the "board" or more
formally the "substrate". �This is usually made out of epoxy-glass,
which is usually a material called "FR-4". �The "FR" in "FR-4" stands
for "fire retardant", it probably refers to the epoxy used, and it's
probably not what people really use any more. �Cheaper consumer goods
use a phenolic paper board -- it's what you'll find in clock radios and
the like. �It's weaker, it burns at a lower temperature, and it smells
funny when it gets hot. �It's also extremely cost effective if you don't
ask too much of it. �Really expensive equipment may use Teflon-glass or
ceramic for a substrate, but I doubt you'll see that in any consumer
equipment.

The metal part is made of copper, it form the circuitry and each 'wire'
is called a 'trace'. �AFAIK it's made by plating onto the board.

Boards can be:

- Single-layer, single-sided (cheap clock radios, again): �All the
traces are all on one side. �This is very inexpensive to produce, but
the layout of the traces is very constrained.

- Single-layer, double-sided (probably what you have): �There are traces
on both sides, and most of the holes are plated on the inside so a
circuit can be carried from the top side to the bottom. �More expensive,
but quite versatile.

- Multi-layer: �This is built up from a bunch of really thin
double-sided boards that are glued together in a special press. �I am
_not_ up on the whole process, but if you don't mind spending $$$ you
can have about as many layers made as you're willing to pay for. �The
job of laying out a really tight circuit is considerably eased, but each
layer costs more $$$. �Computer mother boards are often 4 layers, and
it's a miracle that they aren't six or eight or more, given what they
do. �Someone spends a _lot_ of design time on those!

There's a coating over all of the board except the parts that you want
to solder to. �It's called "solder mask" or sometimes "solder resist".
It protects the board from inadvertent solder bridges during
manufacture, and from corrosion afterwards.

All the writing on the board (usually in white paint) is called the
"silk", because it is silk-screened on (actually all the layers are
silk-screened on).

--

Tim Wescott
Wescott Design Serviceshttp://www.wescottdesign.com

Do you need to implement control loops in software?
"Applied Control Theory for Embedded Systems" gives you just what it says.
See details athttp://www.wescottdesign.com/actfes/actfes.html- Hide quoted text -

- Show quoted text -

Do they use FR-4 for high-volume USB doo-dads??
-mpm

To the OP:
If you're going to try to fix this, clean up the mess as best you can.
Determine if you're dealing wth a multilayer board (if so, I would say
"forget it")
But if you luck out and it "is" actually fixable, I strongly suggest
you use an active liquid flux for the repair job. This will make
soldering much easier, given what you have to work with. Do not just
grab a handheld iron and go to town... You can remove the flux
later.

I suspect however your bigger problem is going to be mechanical
stability once you do get the connnector reattached. And as Tim
mentions, high-speed USB devices do get concerned about impedance, but
if you're really careful, you should be able to get "close enough"
with your repairs.

If this device is simply a USB jump drive doo-hickey, for $10 you can
just go buy another one.
(Unless there are critical files on it you need..?) Best of luck. -
mpm
.

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