PCB Electrical Testing

[Ian Bell]

I am based in the UK and currently use a UK PCB manufacturer who actually has the PCBs made in
China. Prices are very good and include electrical testing.

Another UK company (PCB Train) offers similar prices for PCBs fabricated in the UK except they do
not include electrical testing - with electrical testing included they are far more expensive than
my current supplier.

Now, given that my PCBs are double sided, rather simple tube (valve) based designs, would I be
making any serious compromise by buying PCBs that have not been electrically tested?

Cheers

Ian

 

[Gerard Bok]

I am based in the UK and currently use a UK PCB manufacturer who actually has the PCBs made in
China. Prices are very good and include electrical testing.

Another UK company (PCB Train) offers similar prices for PCBs fabricated in the UK except they do
not include electrical testing - with electrical testing included they are far more expensive than
my current supplier.

Now, given that my PCBs are double sided, rather simple tube (valve) based designs, would I be
making any serious compromise by buying PCBs that have not been electrically tested?

How much would you save on 'going untested' ?
What would it cost you if you get, say, 1% faulty boards ?

 

[Ian Bell]

How much would you save on 'going untested' ?

In the quantities I use it costs and additional 25%.

What would it cost you if you get, say, 1% faulty boards ?

Presumably 1%.

Cheers

Ian

 

[[email protected]]

I am based in the UK and currently use a UK PCB manufacturer who actually has the PCBs made in
China. Prices are very good and include electrical testing.

Another UK company (PCB Train) offers similar prices for PCBs fabricated in the UK except they do
not include electrical testing - with electrical testing included they are far more expensive than
my current supplier.

Now, given that my PCBs are double sided, rather simple tube (valve) based designs, would I be
making any serious compromise by buying PCBs that have not been electrically tested?

Electrical testing itself shouldn't be *that* expensive. It depends on what
your fallout rate would be and the cost of the assembly. If your board is of
any complexity at all (large number of traces and vias, fine pitch traces,
etc.) your fallout rate could be substantial. The added cost could be because
they know they'll have to eat a lot of boards, rather than the actual cost of
testing. That would certainly bust your cost curve, considering that you'll
be throwing away finished product instead of just raw boards (as they would
be). Find someone else.

 

[[email protected]]

In the quantities I use it costs and additional 25%.



Presumably 1%.

We get a lot more than 1% "x-outs" on even our small boards and we don't see
completely bad panels.

 

[John Devereux]

I am based in the UK and currently use a UK PCB manufacturer who
actually has the PCBs made in China. Prices are very good and include
electrical testing.

Another UK company (PCB Train) offers similar prices for PCBs
fabricated in the UK except they do not include electrical testing -
with electrical testing included they are far more expensive than my
current supplier.

Now, given that my PCBs are double sided, rather simple tube (valve)
based designs, would I be making any serious compromise by buying PCBs
that have not been electrically tested?

Hi Ian,

I always specify BBT for production boards, since it costs so much (in
time and effort) to fix faults. Sometimes you will be lucky and get zero
failures in a few hundred boards - but sometimes there will be 10% and
that is a lot of boards to scrap/repair. Depends a bit on the design
rules and the supplier of course.

It seems there are two types of board testing. One type ("flying probe")
costs me ~£60 setup and ~40p per board to test. The other ("bed of
nails") is ~£200 setup but zero per board.

For prototypes I don't bother, since I will likely spend so much time on
them anyway and the quantities are so low that the BBT setup looks very
expensive as a "per board" cost. I can't remember ever having a problem
on a "prototype" quantity order (say 1-5 pcs). Perhaps they test these
anyway, don't know.

 

[Ian Bell]

Electrical testing itself shouldn't be *that* expensive. It depends on what
your fallout rate would be and the cost of the assembly. If your board is of
any complexity at all (large number of traces and vias, fine pitch traces,
etc.) your fallout rate could be substantial. The added cost could be because
they know they'll have to eat a lot of boards, rather than the actual cost of
testing. That would certainly bust your cost curve, considering that you'll
be throwing away finished product instead of just raw boards (as they would
be). Find someone else.

I already have someone else who does do electrical test. My only reason for considering changing was
to support a local company during the current bad times.

Cheers

Ian

 

[[email protected]]

I already have someone else who does do electrical test. My only reason for considering changing was
to support a local company during the current bad times.

Ok, you've fixed the expense of building up from defective boards but you
still have no idea what your fallout will be. Unless this is an incredibly
simple board with very relaxed groundrules, I'm sure it will be much greater
than your 1%. Yeah, if it were only a few dimes it might be good to support
the local guy, as long as you can make it and your quality doesn't suffer.

 

[[email protected]]

Hi Ian,

I always specify BBT for production boards, since it costs so much (in
time and effort) to fix faults. Sometimes you will be lucky and get zero
failures in a few hundred boards - but sometimes there will be 10% and
that is a lot of boards to scrap/repair. Depends a bit on the design
rules and the supplier of course.

It seems there are two types of board testing. One type ("flying probe")
costs me ~£60 setup and ~40p per board to test. The other ("bed of
nails") is ~£200 setup but zero per board.

Those costs are *highly* dependant on the complexity of the board. We have
one where they laughed at us for suggesting bed-of-nails.

For prototypes I don't bother, since I will likely spend so much time on
them anyway and the quantities are so low that the BBT setup looks very
expensive as a "per board" cost. I can't remember ever having a problem
on a "prototype" quantity order (say 1-5 pcs). Perhaps they test these
anyway, don't know.

Again, that depends on the complexity. As you note above, troubleshooting and
repairing boards is *very* expensive, ten times so on an unknown design.

 

[Ian Bell]

Ok, you've fixed the expense of building up from defective boards but you
still have no idea what your fallout will be. Unless this is an incredibly
simple board with very relaxed groundrules, I'm sure it will be much greater
than your 1%. Yeah, if it were only a few dimes it might be good to support
the local guy, as long as you can make it and your quality doesn't suffer.

Indeed, if the total cost difference including fallouts was small it would be worth it. I was hoping
to get some idea of what the typical insdustry fall out rate is.

Cheers

Ian

 

[Ian Bell]

Those costs are *highly* dependant on the complexity of the board. We have
one where they laughed at us for suggesting bed-of-nails.


Again, that depends on the complexity. As you note above, troubleshooting and
repairing boards is *very* expensive, ten times so on an unknown design.

As I mentioned in my origin al post, these boards are really quite simple. All through hole
components and minimum track size 25 thou/mil. Does that make a significant diffiernce to the fall
out rate?

Cheers

ian

 

[John Devereux]

Those costs are *highly* dependant on the complexity of the board. We have
one where they laughed at us for suggesting bed-of-nails.


Again, that depends on the complexity. As you note above, troubleshooting and
repairing boards is *very* expensive, ten times so on an unknown design.

Sure, perhaps I should have said that I was talking about two-layer
boards only (Ians' "rather simple tube designs"). My supplier always
tests 4+ layer boards anyway as part of their process. Even if they
didn't I would get them tested since they would likely be always
impractical to repair, what with the hidden internal planes and all.

 

[Rich Grise]

I am based in the UK and currently use a UK PCB manufacturer who actually
has the PCBs made in China. Prices are very good and include electrical
testing.

Another UK company (PCB Train) offers similar prices for PCBs fabricated
in the UK except they do not include electrical testing - with electrical
testing included they are far more expensive than my current supplier.

Now, given that my PCBs are double sided, rather simple tube (valve) based
designs, would I be making any serious compromise by buying PCBs that have
not been electrically tested?

If it ain't broke, don't fix it.

Cheers!
Rich

 

[John Devereux]

As I mentioned in my origin al post, these boards are really quite
simple. All through hole components and minimum track size 25
thou/mil. Does that make a significant diffiernce to the fall out
rate?

Those are very "generous" design rules. I normally use 8 thou, my
supplier will do down to 5 thou without charging extra. However some of
the defects I have seen on untested boards would still create failures
even with your rules. For example very occasionally there are things
that look like "scratches" cutting several parallel tracks. But usually
it is single track cuts or shorts.

But yes I think the difference is significant. I think you could risk
it. I stuck with untested boards for quite a long time before I gave up
on them and paid the extra, And this was with <8 thou rules and probably
more complicated boards than yours.

 

[[email protected]]

Correction: laughed at us for suggesting a "flying probe" test. It would
have taken all day.

As I mentioned in my origin al post, these boards are really quite simple. All through hole
components and minimum track size 25 thou/mil. Does that make a significant diffiernce to the fall
out rate?

Sure, that's three times the width of a normal trace. You only have a
two-sided board, another key advantage. Considering that you will do an
electrical test before populating the board your favored supplier might be a
good bet.

 

[Ian Bell]

Those are very "generous" design rules. I normally use 8 thou, my
supplier will do down to 5 thou without charging extra. However some of
the defects I have seen on untested boards would still create failures
even with your rules. For example very occasionally there are things
that look like "scratches" cutting several parallel tracks. But usually
it is single track cuts or shorts.

But yes I think the difference is significant. I think you could risk
it. I stuck with untested boards for quite a long time before I gave up
on them and paid the extra, And this was with<8 thou rules and probably
more complicated boards than yours.

I remember getting lots of those in 'the old days' (30 years ago) and they were mostly due to human
hairs introduced in the photographic process. I would have thought with CAD this would no longer occur.

Cheers

Ian

 

[Ian Bell]

If it ain't broke, don't fix it.

Cheers!
Rich

Indeed. My only motivation in these hard times was to try to place more work locally.

Cheers

ian

 

[John Devereux]

Ian Bell<[email protected]> writes:

[...]

Those are very "generous" design rules. I normally use 8 thou, my
supplier will do down to 5 thou without charging extra. However some of
the defects I have seen on untested boards would still create failures
even with your rules. For example very occasionally there are things
that look like "scratches" cutting several parallel tracks. But usually
it is single track cuts or shorts.

But yes I think the difference is significant. I think you could risk
it. I stuck with untested boards for quite a long time before I gave up
on them and paid the extra, And this was with<8 thou rules and probably
more complicated boards than yours.

I remember getting lots of those in 'the old days' (30 years ago) and
they were mostly due to human hairs introduced in the photographic
process. I would have thought with CAD this would no longer occur.

It only happened a few times, and only on ~one board per batch. I
guessed they might be scratches on the boards photo resist (rather than
on the master photoplot).

But hairs work too

 

[Nial Stewart]

I am based in the UK and currently use a UK PCB manufacturer who actually has the PCBs made in

China. Prices are very good and include electrical testing.

Another UK company (PCB Train) offers similar prices for PCBs fabricated in the UK except they do
not include electrical testing - with electrical testing included they are far more expensive than
my current supplier.

Now, given that my PCBs are double sided, rather simple tube (valve) based designs, would I be
making any serious compromise by buying PCBs that have not been electrically tested?

Ian,

Are you talking about production or prototype quantities?

All the boards I build are prototypes. I'll always specify electrical test as I
want to be debugging my design, not boards or the build (I use a good, not cheap
assembly house).

I tend to use Kelan (who have recently been bought over) for these boards. They have beaten
chinese build prices for 10 offs on reasonably complex (6/8 layer) boards
so it might be worth getting them to quote. They are a 'proper' board house,
not a pile em high operation like PCB train.

www.kelan.co.uk

Hope this helps,


Nial

 

[Uwe Hercksen]

Now, given that my PCBs are double sided, rather simple tube (valve)
based designs, would I be making any serious compromise by buying PCBs
that have not been electrically tested?

Hello,

if your boards have a low trace density, wide traces and wide isolation
gaps, few pins and vias with larger hole diameters the probability of
electrical errors should be low.

Bye