> On 29 ene, 17:04, LittleAlex <alex.lo...@email.com> wrote:
>> On Jan 28, 11:40 pm, nna...@terra.es wrote:
>>
>> > INCREDIBLE!!
>> > the problem on a new series PCB, the prototype worked well but in the
>> > last version there was some resistance or short circuit in the bus
>> > lines wich hangued the cpu and possibly destroyed the XCS05 (with
>> > strange white or black substance going out of the gnd or vcc pins).
>> > With a 5V supply between the line and GND we eliminated the shorts
>> > but
>> > appeared after few minutes. We try to measure the resistance of the
>> > lines with a tester and found to be lower and lower, accelerating the
>> > decrease if we heated the PCB. Anybody knows the explanation of that
>> > ?
>> > thank you
>>
>> > Narcis Nadal
>>
>> I have seen something like this before.
>>
>> In my case, the PCB laminate was slightly porous, and the tin plating
>> oozed into cracks. I would set me bench supply to 5V, and up the
>> current limit until I burned them out. I would need to repeat this
>> ever other day until I got new PCB's in.
>>
>> AL
>
> I don't know if it is foam but is so dense. We speculate about heated
> flux. Arround the "resistance" of the tracks, can be possible for a
> liquid proceeding from the manufacture of the pcb to stay unther the
> green barnish ? If it where an acid there were possible to change the
> resistance with the temperature and the copper ? Is possible to do
> something similar with defluxer drained in a via and interacting with
> something inside the pcb?
>
> Thank you
> Narcis Nadal
The black substance could be melted IC casing plastic, if the ICs are
getting hot enough. I once had a lamp power cord short out, due to
excessive flexing cracking the synthetic-rubber insulation. Some of the
rubber insulation was transformed into a viscous green liquid, which
remained liquid even after everything cooled down. Apparently the heat
had triggered a chemical reaction between the insulation and the copper
wiring, hence the green color.
--
John F. Eldredge -- john@jfeldredge.com
PGP key available from http://pgp.mit.edu
"Reserve your right to think, for even to think wrongly is better
than not to think at all." -- Hypatia of Alexandria
Reply by LittleAlex●January 30, 20092009-01-30
On Jan 29, 2:51 pm, David Brown
<david.br...@hesbynett.removethisbit.no> wrote:
> LittleAlex wrote:
> > On Jan 28, 11:40 pm, nna...@terra.es wrote:
> >> INCREDIBLE!!
> >> the problem on a new series PCB, the prototype worked well but in the
> >> last version there was some resistance or
> >> short circuit in the bus lines wich hangued the cpu and possibly
> >> destroyed the XCS05 (with strange white or black substance going out
> >> of the gnd or vcc pins).
> >> With a 5V supply between the line and GND we eliminated the shorts
> >> but
> >> appeared after few minutes. We try to measure the resistance of the
> >> lines with a tester and found to be lower and lower, accelerating the
> >> decrease if we heated the PCB. Anybody knows the explanation of
> >> that ?
> >> thank you
>
> >> Narcis Nadal
>
> > I have seen something like this before.
>
> > In my case, the PCB laminate was slightly porous, and the tin plating
> > oozed into cracks. I would set me bench supply to 5V, and up the
> > current limit until I burned them out. I would need to repeat this
> > ever other day until I got new PCB's in.
>
> Wouldn't it work better with a higher voltage supply (with a large
> current capability) to more permanently blow out the shorts? It would
> also make it easier to see where the problems are (look for the black
> marks!).
The theory was that anything over 5V would let the magic smoke out of
the IC's. I was doing this to stuffed boards.
AL
Reply by ●January 30, 20092009-01-30
On 29 ene, 17:04, LittleAlex <alex.lo...@email.com> wrote:
> On Jan 28, 11:40 pm, nna...@terra.es wrote:
>
> > INCREDIBLE!!
> > the problem on a new series PCB, the prototype worked well but in the
> > last version there was some resistance or
> > short circuit in the bus lines wich hangued the cpu and possibly
> > destroyed the XCS05 (with strange white or black substance going out
> > of the gnd or vcc pins).
> > With a 5V supply between the line and GND we eliminated the shorts
> > but
> > appeared after few minutes. We try to measure the resistance of the
> > lines with a tester and found to be lower and lower, accelerating the
> > decrease if we heated the PCB. Anybody knows the explanation of
> > that ?
> > thank you
>
> > Narcis Nadal
>
> I have seen something like this before.
>
> In my case, the PCB laminate was slightly porous, and the tin plating
> oozed into cracks. =A0I would set me bench supply to 5V, and up the
> current limit until I burned them out. =A0I would need to repeat this
> ever other day until I got new PCB's in.
>
> AL
I don't know if it is foam but is so dense. We speculate about heated
flux. Arround the "resistance" of the tracks, can be possible for a
liquid proceeding from the manufacture of the pcb to stay unther the
green barnish ? If it where an acid there were possible to change the
resistance with the temperature and the copper ? Is possible to do
something similar with defluxer drained in a via and interacting with
something inside the pcb?
Thank you
Narcis Nadal
Reply by Stephen Pelc●January 29, 20092009-01-29
On Thu, 29 Jan 2009 23:01:08 +0100, Falk Willberg
<Faweglassenlk@falk-willberg.de> wrote:
>In order to remove the short circuits on my homebrew PCBs I used an old
>2200uF Capacitor and his maximum rated voltage (~30V).
When I worked in an old (Strowger) telephone exchange, the 50v bus
bars were huge, and we did everything on live equipment. When
a pice of wirewrap (remember when you wire-wrapped with Lindstrom
pliers) wire fell into the frame, we just changed the rack fuses
for something unmentionably large.
The day a spanner fell across the bus bars was memorable. A single
cell of the exchange battery was a cube about 5 feet in each
dimension!
Stephen
--
Stephen Pelc, stephenXXX@mpeforth.com
MicroProcessor Engineering Ltd - More Real, Less Time
133 Hill Lane, Southampton SO15 5AF, England
tel: +44 (0)23 8063 1441, fax: +44 (0)23 8033 9691
web: http://www.mpeforth.com - free VFX Forth downloads
Reply by Falk Willberg●January 29, 20092009-01-29
David Brown schrieb:
> LittleAlex wrote:
...
>> In my case, the PCB laminate was slightly porous, and the tin plating
>> oozed into cracks. I would set me bench supply to 5V, and up the
>> current limit until I burned them out. I would need to repeat this
>> ever other day until I got new PCB's in.
>>
>
> Wouldn't it work better with a higher voltage supply (with a large
> current capability) to more permanently blow out the shorts? It would
> also make it easier to see where the problems are (look for the black
> marks!).
In order to remove the short circuits on my homebrew PCBs I used an old
2200uF Capacitor and his maximum rated voltage (~30V).
Falk
Reply by David Brown●January 29, 20092009-01-29
LittleAlex wrote:
> On Jan 28, 11:40 pm, nna...@terra.es wrote:
>> INCREDIBLE!!
>> the problem on a new series PCB, the prototype worked well but in the
>> last version there was some resistance or
>> short circuit in the bus lines wich hangued the cpu and possibly
>> destroyed the XCS05 (with strange white or black substance going out
>> of the gnd or vcc pins).
>> With a 5V supply between the line and GND we eliminated the shorts
>> but
>> appeared after few minutes. We try to measure the resistance of the
>> lines with a tester and found to be lower and lower, accelerating the
>> decrease if we heated the PCB. Anybody knows the explanation of
>> that ?
>> thank you
>>
>> Narcis Nadal
>
> I have seen something like this before.
>
> In my case, the PCB laminate was slightly porous, and the tin plating
> oozed into cracks. I would set me bench supply to 5V, and up the
> current limit until I burned them out. I would need to repeat this
> ever other day until I got new PCB's in.
>
Wouldn't it work better with a higher voltage supply (with a large
current capability) to more permanently blow out the shorts? It would
also make it easier to see where the problems are (look for the black
marks!).
Reply by -jg●January 29, 20092009-01-29
On Jan 30, 5:47=A0am, "John B" <spamj_baraclo...@blockerzetnet.co.uk>
wrote:
We have struck some field reliability issues we suspect is tin
whiskers/ fretting corrosion on PLCC sockets. - the joys of RoHS
indeed.... :(
-jg
Reply by -jg●January 29, 20092009-01-29
On Jan 29, 7:40=A0pm, nna...@terra.es wrote:
> INCREDIBLE!!
> the problem on a new series PCB, the prototype worked well but in the
> last version there was some resistance or
> short circuit in the bus lines wich hangued the cpu and possibly
> destroyed the XCS05 (with strange white or black substance going out
> of the gnd or vcc pins).
> With a 5V supply between the line and GND we eliminated the shorts
> but
> appeared after few minutes. We try to measure the resistance of the
> lines with a tester and found to be lower and lower, accelerating the
> decrease if we heated the PCB. Anybody knows the explanation of
> that ?
> thank you
>
> Narcis Nadal
Rodent urine ?
-jg
Reply by John B●January 29, 20092009-01-29
On 29/01/2009 nnadal@terra.es wrote:
>
> INCREDIBLE!!
> the problem on a new series PCB, the prototype worked well but in the
> last version there was some resistance or
> short circuit in the bus lines wich hangued the cpu and possibly
> destroyed the XCS05 (with strange white or black substance going out
> of the gnd or vcc pins).
> With a 5V supply between the line and GND we eliminated the shorts
> but
> appeared after few minutes. We try to measure the resistance of the
> lines with a tester and found to be lower and lower, accelerating the
> decrease if we heated the PCB. Anybody knows the explanation of
> that ?
> thank you
>
> Narcis Nadal
> INCREDIBLE!!
> the problem on a new series PCB, the prototype worked well but in the
> last version there was some resistance or
> short circuit in the bus lines wich hangued the cpu and possibly
> destroyed the XCS05 (with strange white or black substance going out
> of the gnd or vcc pins).
> With a 5V supply between the line and GND we eliminated the shorts
> but
> appeared after few minutes. We try to measure the resistance of the
> lines with a tester and found to be lower and lower, accelerating the
> decrease if we heated the PCB. Anybody knows the explanation of
> that ?
> thank you
>
> Narcis Nadal
I have seen something like this before.
In my case, the PCB laminate was slightly porous, and the tin plating
oozed into cracks. I would set me bench supply to 5V, and up the
current limit until I burned them out. I would need to repeat this
ever other day until I got new PCB's in.
AL