Reverse polarity, Scotty.

[Phil Hobbs]

Hi all,

Because of a miscommunication with a client's layout person, I find
myself in need of a series-connected dual Schottky diode in SC70 whose
pinout is opposite to the BAV54SW, i.e. I need something like this:


*------*
K ==| |
| |== COM
A ==| |
*------*

It'll be used at 20 mA, 12V, no inductive kick. I can use the BAV99RW,
but that'll cost me a volt's worth of drop, which I'd rather avoid. Any
suggestions?

Thanks

Phil Hobbs
--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510

hobbs at electrooptical dot net
http://electrooptical.net

 

[RobertMacy]

Hi all,

Because of a miscommunication with a client's layout person, I find
myself in need of a series-connected dual Schottky diode in SC70 whose
pinout is opposite to the BAV54SW, i.e. I need something like this:


*------*
K ==| |
| |== COM
A ==| |
*------*

It'll be used at 20 mA, 12V, no inductive kick. I can use the BAV99RW,
but that'll cost me a volt's worth of drop, which I'd rather avoid. Any
suggestions?

Thanks

Phil Hobbs

If you can stand the overhead, put the BAV54SW on a little 'sub' PCB and
stick that down.

 

[Joerg]

Hi all,

Because of a miscommunication with a client's layout person, I find
myself in need of a series-connected dual Schottky diode in SC70 whose
pinout is opposite to the BAV54SW, i.e. I need something like this:


*------*
K ==| |
| |== COM
A ==| |
*------*

It'll be used at 20 mA, 12V, no inductive kick. I can use the BAV99RW,
but that'll cost me a volt's worth of drop, which I'd rather avoid. Any
suggestions?

Before time runs out too far I'd consider a re-layout. The only series
Schottky I ever saw in an "oops" package was SOT23, and that was a while
ago and an RF part that IIRC didn't take 12V.

To get product tested and maybe even into the field (via deviation) you
could have them hand-soldered reversed for cathode/anode, sort of
standing at a 45 degree angle, and then have COM handwired.

 

[Lasse Langwadt Christensen]

Or make a little "daughter" board.

an SC70 is 2x2mm if there's room for a daughter board there's room for two discrete diodes

simple fix is like Jan suggested; mount it upside down,
might not even need to bend the legs, just be little generous with the solder

-Lasse

 

[Joerg]

Or make a little "daughter" board.

If you have to make a board anyhow, why not fix the real McCoy instead?
It's less effort.

But before that, tear off a page from the "anger pad", crumple, and
chuck it into a corner of the room, with gusto

http://www.flickr.com/photos/28230883@N03/2714686795/
http://www.werswissenwill.de/images/wutzettel_360.gif

For some reason I've never seen those in the US. I remember when we told
our mechanical engineer at my first company that we had a "slight"
change in the mold for a plastic part and at that point he really needed
this pad.

 

[Phil Hobbs]

Before time runs out too far I'd consider a re-layout. The only series
Schottky I ever saw in an "oops" package was SOT23, and that was a while
ago and an RF part that IIRC didn't take 12V.

To get product tested and maybe even into the field (via deviation) you
could have them hand-soldered reversed for cathode/anode, sort of
standing at a 45 degree angle, and then have COM handwired.

Thanks, I didn't see any either. However, happily it looks like the
BAV99RW will work okay. I may need to make the 47 uF cap a little
bigger to compensate for the extra voltage drop, but oh well.

If there needs to be a spin for other reasons we'll go back to the
BAT54Ses. Right now we have to figure out how to get the board clean
enough. I really miss PbSn!

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510

hobbs at electrooptical dot net
http://electrooptical.net

 

[Joerg]

Thanks, I didn't see any either. However, happily it looks like the
BAV99RW will work okay. I may need to make the 47 uF cap a little
bigger to compensate for the extra voltage drop, but oh well.

If there needs to be a spin for other reasons we'll go back to the
BAT54Ses. Right now we have to figure out how to get the board clean
enough. I really miss PbSn!

A RoHS board? My condolences. If it's any comfort I'll have one of those
coming up in fall 2014. The bureaucrats in Brussels took away the
exemption for medical. Hurumph. Grumble.

Make sure there is a liability waiver in your agreement for when the
lead-free stuff fails in the field.

 

[Joerg]

Could you translate, please?

ANGER SHEET .. Crumple in case of anger attack and chuck into a corner.

(in German a corner in this context means the corner of a room)

I agree that it's best to just bite the bullet and lay the board out
anew. Sometimes it's worthwhile to build up a first article anyway, with
lots of green wires (or upside-down components), but in the end it's best
to just get it right.

Yup.


(What is it about diodes that they appear to be cursed? When you're not
getting boards back from the assembly house with the two-lead diodes in
backwards, you're getting layouts back from he layout house with three-
lead diodes all cockeyed).

I just had one with a 2-pad SMT diode reversed because the layouter
scooted the "C" mark to far. And here I thought they'd always go by the
CAD file. Oh well, happens.

 

[[email protected]]

ANGER SHEET .. Crumple in case of anger attack and chuck into a corner.

(in German a corner in this context means the corner of a room)



I just had one with a 2-pad SMT diode reversed because the layouter
scooted the "C" mark to far. And here I thought they'd always go by the
CAD file. Oh well, happens.

At a PPoE the layout guy was always getting diodes backwards. He
ASSUMEd that pin AO1 was the cathode. "It's IPC standards."
Unfortunately, not all diode manufacturers got the memo. We
eventually solved the problem by using 'C' and 'A' for the library pin
names (for arrays that becomes "C01" and "A01").

 

[[email protected]]

A RoHS board? My condolences. If it's any comfort I'll have one of those
coming up in fall 2014. The bureaucrats in Brussels took away the
exemption for medical. Hurumph. Grumble.

Make sure there is a liability waiver in your agreement for when the
lead-free stuff fails in the field.

I've been using socialist solder processes for five years. After they
got the paste/stencil and temperature profiles right, I haven't seen
any problems. Nothing from the field.

 

[Joerg]

I've been using socialist solder processes for five years. After they
got the paste/stencil and temperature profiles right, I haven't seen
any problems. Nothing from the field.

Five years in the field is not a long time. It also depends on how it is
used, harsh environments, vibrations and so on. It's not just issues
that can develop with IC packages, also with passives:

http://www.calce.umd.edu/articles/openart/Page_2_Flex_Cracking.pdf

 

[[email protected]]

Hi all,



Because of a miscommunication with...

whatever..you need Style 10:

http://www.onsemi.com/pub_link/Collateral/419-04.PDF

not available in smallish 30V VR which I assume is what your after.

 

[Nico Coesel]

Thanks, I didn't see any either. However, happily it looks like the
BAV99RW will work okay. I may need to make the 47 uF cap a little
bigger to compensate for the extra voltage drop, but oh well.

If there needs to be a spin for other reasons we'll go back to the
BAT54Ses. Right now we have to figure out how to get the board clean
enough. I really miss PbSn!

Make sure they solder it in a nitrogen atmosphere. The joints will
look just as good as with leaded solder.

 

[George Herold]

I have a customer who wants us to use a stack of fairly rigid Bergquist thermal
pad gunk, about the consistancy of used bubble gum, to transfer heat from a pcb,
between the bottom of the board and the extruded enclosure. Bergquist wants
something like 20% compression, which would bow our board like a potato chip and
probably pop the BGA balls.

Can you put pads both top and bottom? Maybe only 10% compression on each side? (D@mn the expense and full steam ahead.)

George H.

 

[Spehro Pefhany]

Usually you can bend the leads once without problems. drop of solder does the rest.
Else, as somebody already pointed out, make small adapter boards.

I've never had any luck bending the leads on those little SMT
packages- they tend to break right off. I'd stick it on upside down
with blobs of solder re-inforced with little single strands from
stranded wire, if necessary. Okay for up to a few dozen pieces, with
some small loss in dignity, reliability etc.

Yes that is usually small signal stuff.



It is impressive....
30ms is not that fast, is there not a normal small bridge rectifier (no Schottky)
that you could solder, I had some small round ones with wires coming out, 30V 50 Hz.

Best regards,
Spehro Pefhany

 

[[email protected]]

Use schematic symbols that match the part... complete with the "dent"
marking pin 1 ;-)

That does nothing. The schematic already has the anode and cathode
clearly marked. The real problem is that the pick-n-place machines
can't read the schematics, only the footprint.

 

[[email protected]]

Five years in the field is not a long time. It also depends on how it is
used, harsh environments, vibrations and so on. It's not just issues
that can develop with IC packages, also with passives:

http://www.calce.umd.edu/articles/openart/Page_2_Flex_Cracking.pdf

I've seen leads pulled off components but no failed solder joints. The
gloom and doom from five years ago was that commie solder wouldn't
make a year without tin whiskers. None so far.

 

[Joerg]

That does nothing. The schematic already has the anode and cathode
clearly marked. The real problem is that the pick-n-place machines
can't read the schematics, only the footprint.

They should be reading the CAD file. Older ones needed a XYRS file for that.

 

[George Herold]

No, there are all sorts of parts on the top, and the top cover of the

box slides on/off horizontally.
The silly thing is that I proved to them that the d@mn thing is fine,

thermally, as designed. Somebody put their finger on the FPGA, thought
it felt hot, and things escalated.
I note, in passing, that most peoples' instincts about thermal things,
suck.

Oh my.. tell me about it! (no thermal instincts)
I keep trying to 'wash my hands' of the current project.
(I worry a bit that it'll get me fired.)
At the heart is a LN2 cryostat. My boss thinks more mass is better, 'causethen the temperature will be stable... As it stands now the probe must have several pounds of copper. Byzantine layers are added to try and correct a 'flawed' design. I guesstimated a time constant of ~1000 seconds with 100 Watts of heater power for one internal structure. When I try and talk about low mass, fast designs, it's like I'm speaking a foreign language.

George H.

 

[Joerg]

I've seen leads pulled off components but no failed solder joints. The
gloom and doom from five years ago was that commie solder wouldn't
make a year without tin whiskers. None so far.

According to Hughes it even brought down one of their satellites:

http://web.archive.org/web/20090303130808/http://www.wirelessweek.com/article.aspx?id=104090