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Solder paste layer padstack, remove for DNF components?

M

markp

Jan 1, 1970
0
Hi All,

I have a component on a PCB that is simply a set of pads with no component
fitted. The idea is that the processor will be fitted pre-programmed, but if
I ever want to change the firmware any existing boards can be re-programmed
using a test pin header using spring type contacts. This keeps the cost down
of the main board by not requiring a header while still gives the ability to
easily re-program.

Question: In the CAD I have padstacks that define the solder paste. I
obviously don't want solder paste on these pads, so is it my responsibility
to remove the solder paste layer for this component and give the assembly
house the final stencil gerbers, or does the assembly house modify them to
produce their own stensils? If the latter I presume they would also not
paste un-fitted components. What is the normal way things are done?

Mark.
 
M

markp

Jan 1, 1970
0
TTman said:
You send them the gerber layer for the stencil as you want it. They will
send that away to have the stencil made in the appropriate thickness (
thinness!)

OK, so presumably any do not fit components would end up being pasted and a
layer of solder ends up on the pads, unless I explicitly remove the mask
from the solder paste gerber?
 
M

markp

Jan 1, 1970
0
TTman said:
Also, if you can program/upgrade the CPU with ISP, why not have it fitted
at assembly time and program it when you get the board back. The cost of
ISP must be much less than soldering on by hand a CPU...

The CPUs are ISP devices that pre-programmed by a programming house
(automatically de-reeled, programmed, and re-reeled. Quite cheap to do
that). The board is quite simple, and it will be tested in situ when it is
assembled with other boards. So the cost of explicitly programming each one
(thousands off) is quite high. However, I don't want to write off any boards
that had been made already should i find I needed to change the firmware, so
that's why it has pads only. To add an explicit programming header would add
cost for a function thay will hopefully never be used.

Mark.
 
C

Charlie E.

Jan 1, 1970
0
The CPUs are ISP devices that pre-programmed by a programming house
(automatically de-reeled, programmed, and re-reeled. Quite cheap to do
that). The board is quite simple, and it will be tested in situ when it is
assembled with other boards. So the cost of explicitly programming each one
(thousands off) is quite high. However, I don't want to write off any boards
that had been made already should i find I needed to change the firmware, so
that's why it has pads only. To add an explicit programming header would add
cost for a function thay will hopefully never be used.

Mark.

Mark,
Just curious, what spring loaded connector are you using to program
these boards? I am currently working on a board, and have found that
I need to connect to it to program it in situ. I am presently going
to just try having through hole pins that will provide a tight fit to
a .100 connector stuck through them, but wondered if there is a better
way?

Charlie
 
S

Spehro Pefhany

Jan 1, 1970
0
Mark,
Just curious, what spring loaded connector are you using to program
these boards? I am currently working on a board, and have found that
I need to connect to it to program it in situ. I am presently going
to just try having through hole pins that will provide a tight fit to
a .100 connector stuck through them, but wondered if there is a better
way?

Charlie

Microchip has a connector design that requires only pads and holes on
the PCB.

http://www.microchip.com/stellent/idcplg?IdcService=SS_GET_PAGE&nodeId=1406&dDocName=en541943

I haven't tried it. Some other folks have come up with a row of pogo
pins that can be held against an unpopulated row of 1x6 0.1" header
holes (the header is probably the most popular connector scheme for
low volumes). Or a PCB fixture can be designed with pogo pins that
actually holds the PCB in alignment and avoids having the get your
hands near the programming cable.



Best regards,
Spehro Pefhany
 
M

markp

Jan 1, 1970
0
Mark,
Just curious, what spring loaded connector are you using to program
these boards? I am currently working on a board, and have found that
I need to connect to it to program it in situ. I am presently going
to just try having through hole pins that will provide a tight fit to
a .100 connector stuck through them, but wondered if there is a better
way?

Charlie

Mark,
Just curious, what spring loaded connector are you using to program
these boards? I am currently working on a board, and have found that
I need to connect to it to program it in situ. I am presently going
to just try having through hole pins that will provide a tight fit to
a .100 connector stuck through them, but wondered if there is a better
way?

Charlie

As others have noted these are 'pogo' pins, although I think Pogo is a trade
name and uses synonymously with this kind of bed of nails pin (like hoover
is used for vacuum cleaners). If you do a search for pogo pins on Farnell
you get some expensive pins, but searching for 'spring test pin' and you get
much cheaper versions.

Farnell part example:
1313683

Mark.
 
B

Boris Mohar

Jan 1, 1970
0
Question: In the CAD I have padstacks that define the solder paste. I
obviously don't want solder paste on these pads, so is it my responsibility
to remove the solder paste layer
What is the normal way things are done?

Mark.

Maybe your pad stack editor can define certain pads not to have solderpaste.
My old Orcad DOS version can. (PCB386+)
 
R

Rich Webb

Jan 1, 1970
0
As others have noted these are 'pogo' pins, although I think Pogo is a trade
name and uses synonymously with this kind of bed of nails pin (like hoover
is used for vacuum cleaners). If you do a search for pogo pins on Farnell
you get some expensive pins, but searching for 'spring test pin' and you get
much cheaper versions.

Farnell part example:
1313683

Mill-Max makes a variety of spring-loaded pins in various lengths and
configurations: http://www.mill-max.com/.

I've successfully done a home-made version with their
0906-0-15-20-76-14-11-0 (Digikey p/n ED8180-ND) soldered through regular
0.062 FR4. (maybe not how it was intended to be used but it worked
great)
 
R

Rich Webb

Jan 1, 1970
0
Go in nice and nasty and edit the gerbers manually before sending them
out to the fab. It's like modifying a binary by hand instead of the
source code.
I would not do this unless it's a proto and even then I'd need to be
drunk. Some might say I'm drunk anyways.

It looks like the non-free versions of ViewMate
http://www.pentalogix.com/ permit editing and then re-saving the
modified Gerber files. Might be the cleanest way to "delete" those pads
from the stencil Gerber.

Note to Pentalogix if you're reading: I would have purchased the damned
thing instead of relying on your free version (useful tool, BTW) but I'm
not interested in a node-locked license.
 
M

markp

Jan 1, 1970
0
Hi All,
Maybe your pad stack editor can define certain pads not to have
solderpaste.
My old Orcad DOS version can. (PCB386+)

Yes, that is now what I've done. I've decided to design the PCB for
production so the paste layer on the padstack for this component has now
been removed. I spoke to an assembly house, they can do anything I want
including masking on the stencil during manufacture or removing them from
the stencil entirely. Best though to be in control, so I've removed it for
them.

Mark.
 
C

Charlie E.

Jan 1, 1970
0
On Thu, 04 Feb 2010 20:25:24 -0800, the renowned Charlie E.


Microchip has a connector design that requires only pads and holes on
the PCB.

http://www.microchip.com/stellent/idcplg?IdcService=SS_GET_PAGE&nodeId=1406&dDocName=en541943

I haven't tried it. Some other folks have come up with a row of pogo
pins that can be held against an unpopulated row of 1x6 0.1" header
holes (the header is probably the most popular connector scheme for
low volumes). Or a PCB fixture can be designed with pogo pins that
actually holds the PCB in alignment and avoids having the get your
hands near the programming cable.



Best regards,
Spehro Pefhany

Thanks, Sphero,
That looks like a good idea, and I may incorporate it in my next
design. I will stick with my present idea for now, as it allows me to
even shut the case and do testing and programming, if it works... ;-)

Charlie
 
M

markp

Jan 1, 1970
0
John Walliker said:
Why are you worried about solder paste on the pads?

Spring loaded test pins make good contact with solder-coated pads.

So much so that one very reputable contract manufacturer I have used
specifically asked for paste to be present on test pads. They find
that the test pins dig into the solder and make more reliable contact
than with bare copper.

John

Interesting. I've thought about this and have now decided to keep the paste!
Thanks, it makes sense.

Mark.
 
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