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'[EE] OK to short non-connected pins?'
2009\04\02@192802 by solarwind

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Hey all, I'm experimenting with my DS18B20 1-wire temperature sensors.
Unfortunately, I have the SOIC packages and no adapter boards so I'll
have to improvise and solder on some wires. Luckily, it's an SOIC-8
pin package and since 1-wire requires a max of 3 wires, the rest are
described in the datasheet as "not connected". Is it ok to short some
of the not-connected pins with the pins that are functional so that it
will be easier to solder?

In this case, does "not connected" mean that they should not be
connected to your board or they are literally not connected to the
chip in any way?

--
solarwind

2009\04\02@194812 by cdb

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:: Is it ok to short some
:: of the not-connected pins with the pins that are functional so
:: that it
:: will be easier to solder?

If the pins are marked N/C on the data sheet then these are just there
to provide package stability for soldering purposes.

If you do need to connect them to other pins - I'd connect them to
ground, as a just incase measure - apart from which to my mind it
feels neater.

If you have thin solder, and access to a vice I suggest - tinning the
wires or components first - if you don't have a vice to hold th eleads
then the trick is to bend your solder up by 90 degrees so it is
vertical to the solder reel - wet your tip and then with a little
practice you'll be able to wipe the wire end across the solder, with
the wire/lead in between the iron bit and the solder.

A dab of solder on the IC pins that need to be soldered - then just
wave the wire reasonably close to the pin, gently apply the iron, and
the pretinned components will join like a flux made in ether!

Colin
--
cdb, spam_OUTcolinTakeThisOuTspambtech-online.co.uk on 3/04/2009

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2009\04\02@204613 by solarwind

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On Thu, Apr 2, 2009 at 6:48 PM, cdb <.....colinKILLspamspam@spam@btech-online.co.uk> wrote:
> If the pins are marked N/C on the data sheet then these are just there
> to provide package stability for soldering purposes.
>
> If you do need to connect them to other pins - I'd connect them to
> ground, as a just incase measure - apart from which to my mind it
> feels neater.
>
> If you have thin solder, and access to a vice I suggest - tinning the
> wires or components first - if you don't have a vice to hold th eleads
> then the trick is to bend your solder up by 90 degrees so it is
> vertical to the solder reel - wet your tip and then with a little
> practice you'll be able to wipe the wire end across the solder, with
> the wire/lead in between the iron bit and the solder.
>
> A dab of solder on the IC pins that need to be soldered - then just
> wave the wire reasonably close to the pin, gently apply the iron, and
> the pretinned components will join like a flux made in ether!

Thanks. I just finished soldering the 3 wires to the chip. It worked
well. The pins on the soic are really weak though...

2009\04\02@214949 by Michael Algernon

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{Quote hidden}

Use some Hot Glue to beef them up.
MA

2009\04\02@223025 by Joseph Bento

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On Apr 2, 2009, at 6:46 PM, solarwind wrote:
>>
>
> Thanks. I just finished soldering the 3 wires to the chip. It worked
> well. The pins on the soic are really weak though...

There are ways to breadboard with SMT parts without a PC board.  Use  
common stripboard or donut board (individual pads).  When you need to  
place a chip, put down a small strip of Kapton tape first, just a bit  
wider than the pin spacing.  Kapton is a high temperature tape,  
transparent, golden brown in color.  Glue the chip to the Kapton with  
a dot of superglue.  Use #30 Kynar wire to route the pins to the  
appropriate pads / traces for your circuit.  0805 components will  
space perfectly between donut pads or stripboard traces.  You may need  
a magnifier lamp to solder individual wires to SOIC pins, but it's  
very doable.  Just practice before soldering a 0.4mm chip.  :-)

Joe

2009\04\02@224900 by solarwind

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On Thu, Apr 2, 2009 at 9:16 PM, Joseph Bento <.....josephKILLspamspam.....kirtland.com> wrote:
> Just practice before soldering a 0.4mm chip.  :-)

0.4 mm, wow, that sounds like a challenge to solder on a normal PCB, lol.

2009\04\03@044657 by Chris Emerson

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On Thu, Apr 02, 2009 at 08:16:53PM -0600, Joseph Bento wrote:
>
> On Apr 2, 2009, at 6:46 PM, solarwind wrote:
> >>
> >
> > Thanks. I just finished soldering the 3 wires to the chip. It worked
> > well. The pins on the soic are really weak though...
>
> There are ways to breadboard with SMT parts without a PC board.  Use  
> common stripboard or donut board (individual pads).

For SOIC, the pin spacing is 0.05", half of the strip spacing.  So the
trick is to cut the strips in half along the holes, and you get
stripboard with SOIC-spaced strips.  Then just solder the SOIC down
normally.  Works well for SOT-23 transistors etc. too.

Cheers,

Chris

2009\04\03@130832 by Sean Breheny

face picon face
It is probably OK to connect N/C pins on an IC to other pins, BUT it
is very important to realize that there are some situations where this
is NOT true.

I once severely damaged a $17000 US device by not insulating wires
which went to some pins marked as "not used". They should have been
more explicit in the data sheet - what they meant was "do not use" not
"internally connected". Sometimes NC means "not connected internally"
other times it means "do not connect". In this case, the extra pins
were test pins used by the factory to calibrate the device.

The longer story is that this was an inertial measurement unit (IMU),
an aerospace navigation device we used in a grad school project. Its
original use was in guided bombs - we used it for an unmanned
helicopter. It had a special 30+ pin connector and no other external
interface. The rest of the case was welded shut. The documentation
listed uses for only about 15 of the pins and just left the rest
unmarked. I think there was a comment saying that these were "not
used".

We purchased a cable from the manufacturer to mate with the 30+ pin
connector. The cable had all of the wires populated. We had tight
space constraints so when we tried to mount the IMU, we found that the
bundle of 30 wires didn't have a small enough bend radius to fit in
the clearance between the top of the IMU and the top of the space in
the vehicle. So, we trimmed the unused wires coming out of the back of
the connector. Since I *thought* they were internally not connected,
and space was so tight, I trimmed them flush with the back of the
connector.

After a few days of use, the system was working fine and then suddenly
it went way out of calibration. In trying to figure out what went
wrong, I noticed that there were signals on the unused pins of the
connector. I also noticed that a few of the cut wire ends had stray
strands of wire, some of which touched each other or the case ground.
I trimmed these but it was too late - the damage was permanent. We
sent the unit back to the factory and it cost $7000 US to repair.

I still think that it was really silly that such a rugged aerospace
device brought out such easily damaged device lines to its external
interface and even more silly that no explicit note was made about NOT
connecting to the extra pins. However, I also learned my lesson to be
extra careful about interpreting what is meant by "unused" or NC pins
on devices.

Sean


On Thu, Apr 2, 2009 at 7:48 PM, cdb <EraseMEcolinspam_OUTspamTakeThisOuTbtech-online.co.uk> wrote:
{Quote hidden}

>

2009\04\03@195140 by Russell McMahon

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> For SOIC, the pin spacing is 0.05", half of the strip spacing.  So the
> trick is to cut the strips in half along the holes, and you get
> stripboard with SOIC-spaced strips.  Then just solder the SOIC down
> normally.  Works well for SOT-23 transistors etc. too.


But, whi is going to hang the bell on the cat? :-)

ie cutting strips in half sounds useful, but potentially interesting in its
own right.

- 'Craft knife' and rule?
- Dremel?
- Other...?


   R

2009\04\03@202258 by Joseph Bento

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On Apr 3, 2009, at 5:26 PM, Russell McMahon wrote:

>> For SOIC, the pin spacing is 0.05", half of the strip spacing.  So  
>> the
>> trick is to cut the strips in half along the holes, and you get
>> stripboard with SOIC-spaced strips.  Then just solder the SOIC down
>> normally.  Works well for SOT-23 transistors etc. too.
>
>
> But, whi is going to hang the bell on the cat? :-)
>
> ie cutting strips in half sounds useful, but potentially interesting  
> in its
> own right.


A Dremel with diamond cutting wheel works.  A sharp Xacto works, but  
slippage and bloody accidents are a possibility as the blade tip slips  
or snaps (I've had both happen).  I'd definitely recommend wearing a  
pair of safety glasses while cutting the strips.

Yes, cutting the strips cleanly is always an issue, which is why I  
usually use the Kapton tape.  Too bad cutting a trace isn't as easy as  
isolating the trace, which just requires a drill bit spinning in your  
fingers.


Joe

2009\04\04@020434 by Vis Naicker

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Subject:
To: "Microcontroller discussion list - Public." <@spam@piclistKILLspamspammit.edu>
Message-ID: <KILLspam7F081EF8-DAAB-4AD3-A570-14981A2B833DKILLspamspamkirtland.com>> Content-Type: text/plain; charset=US-ASCII; format=flowed; delsp=yes


Joseph Bento wrote:
>> When you need to  place a chip, put down a small strip of Kapton
>> tape first, just a bit wider than the pin spacing.  Kapton is a
>> high temperature tape, transparent, golden brown in color.  Glue
>> the chip to the Kapton with a dot of superglue.  Use #30 Kynar
>> wire to route the pins to the appropriate pads / traces for
>> your circuit.  0805 components will space perfectly between donut
>> pads or stripboard traces.  You may need a magnifier lamp to solder
>> individual wires to SOIC pins, but it's very doable.  Just practice
>> before soldering a 0.4mm chip.  :-)

http://elm-chan.org/docs/wire/wiring_e.html
and check out the rest of the site http://elm-chan.org/cc_e.html
High temperature tape can be obtained from Dealextreme
www.dealextreme.com/search.dx/search.%22temperature%20tape%22
I have been meaning to start a blog soon about the items on Dealextreme
that would be hackable for scroungers ...

2009\04\04@022021 by Joseph Bento

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On Apr 4, 2009, at 12:02 AM, Vis Naicker wrote:
>

> Joseph Bento wrote:
>>> When you need to  place a chip, put down a small strip of Kapton
>>> tape first, just a bit wider than the pin spacing.  Kapton is a
>>> high temperature tape, transparent, golden brown in color.  Glue
>>> the chip to the Kapton with a dot of superglue.  Use #30 Kynar
>>> wire to route the pins to the appropriate pads / traces for
>>> your circuit.  0805 components will space perfectly between donut
>>> pads or stripboard traces.  You may need a magnifier lamp to solder
>>> individual wires to SOIC pins, but it's very doable.  Just practice
>>> before soldering a 0.4mm chip.  :-)
>
> http://elm-chan.org/docs/wire/wiring_e.html

Yes!  Very nice!  Looks like my description.  :-)  I should have  
thought to put up a website some time ago!  I'll need to spend some  
time perusing that website.  There's some really useful stuff there!

Thanks for the Dealextreme link.  Their prices are very good!  I still  
have a couple rolls of Kapton I bought at the Dayton Hamvention a  
couple years ago.

Joe

2009\04\04@051014 by Tony Smith

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> High temperature tape can be obtained from Dealextreme
> www.dealextreme.com/search.dx/search.%22temperature%20tape%22
> I have been meaning to start a blog soon about the items on Dealextreme
> that would be hackable for scroungers ...


That DealExtreme tape is pretty good stuff, I've used it in powder coating.
They say it'll handle 200C, but I think that's a typo, 300C (as stated on a
couple of items) is more likely.  I've tested it to 250C.

They've got it in sizes 3-20mm.  There's also an eBay seller (or maybe was)
who'd sell it to you in any width, at least 500mm from memory.

It may leave the adhesive behind if you tear it off too quickly, if it does
just stick it back down an pull it off slowly.

It comes in green as well, the green tape seems to be a bit thicker, and the
adhesive not as aggressive.  

Tony

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