BARE BOARD PCB TEST QUESTION

Hi,

I'm routing a PCB.

I'm trying to figure out if I can reduce the number of nails required
by the fixture that my PCB manufacturer will have to build in order to
test the bare boards.


FACTS
----------
The non recurring cost of PCB bare-board test fixtures depends on:

1) The size of the pads to test (the smaller the more expansive)
2) The number of the pads to test

My boards are 80% SMD and 20% TH


Question 1
----------------
I've been told that PCB makers put one nail every terminal node of a
net. Is that true?


Question 2
----------------
Let's say we got a net which connects 5 SMT pads:


Routing option 1
The net is routed in a way that we have 5 end points

O------------------------------------- O
       |          |          |
       |          |         O
      O        O


Routing option 2
The net is routed in a way that we have 2 end points

O----O--------O--------O------------- O



Routing option 1 requires 5 nails, is that true?

Routing option 2 requires 2 nails, is that true?

Routing option 2 is less expensive than option 1 because requires less
nails, is that true?


thanks in advance for any hints,
Enrico

Enrico wrote:
> I'm trying to figure out if I can reduce the number of nails required
> by the fixture that my PCB manufacturer will have to build in order to
> test the bare boards.
> 
> FACTS
> ----------
> The non recurring cost of PCB bare-board test fixtures depends on:
> 1) The size of the pads to test (the smaller the more expansive)
> 2) The number of the pads to test
3) the spacing between tested pads
4) other "points of interest" that you want to examine
etc.

> My boards are 80% SMD and 20% TH
> 
> Question 1
> ----------------
> I've been told that PCB makers put one nail every terminal node of a
> net. Is that true?

Do you *want* this level of testing?  IME, a "simple" visual
inspection is enough for most boards.  You can put a "postage
stamp" test area on one edge of the board that allows for the
vendor to (destructively) examine things like interlayer
registration, hole plating thickness, etc.  But, even that
isn't usually required.

(you havent mentioned the market you are addressing and
how critical the board quality is -- are you designing
boards that are being used on interplanetary probes?)

> Question 2
> ----------------
> Let's say we got a net which connects 5 SMT pads:
> 
> Routing option 1
> The net is routed in a way that we have 5 end points
> 
> O------------------------------------- O
>        |          |          |
>        |          |          O
>        O          O
> 
> Routing option 2
> The net is routed in a way that we have 2 end points
> 
> O----O--------O--------O------------- O
> 
> Routing option 1 requires 5 nails, is that true?
> Routing option 2 requires 2 nails, is that true?

They only "require" as many test points as *you* are
willing to pay for.  Note option 2 can be more
susceptible to faults (depending on track size, pad
size, etc.) if the tracks are small relative to
the pad size.

You also have to think about how your board will
eventually be serviced.  I.e., how likely are you
to find pads lifted, etc.

> Routing option 2 is less expensive than option 1 because requires less
> nails, is that true?
> 
> thanks in advance for any hints,

Ask yourself (or your client) what level of testing you
*really* need -- and are willing to pay for.  And, ask
your vendor what they will *guarantee* in each different
testing scenario.

Hi

> (you havent mentioned the market you are addressing and
> how critical the board quality is -- are you designing
> boards that are being used on interplanetary probes?)

The market is home alarm systems.
My boards are ordinary 2-layer PCB, nothing special, volumes 10000/
year.


PCB makers charge a non recurring fee for bare PCB tests.
Typical costs range from 500 USD to 1500, that depends on the
dimensions of the SMD and TH pads that are present on board (fine
pitches cost more)

My questions are simple, I guess :-)

1) Do PCB makers test the end points of an electrical net, or they
just test any SMD pad that is attached to the net?

2) Does "Routing option 2" require 2 nails?

3) Does "Routing option 1" require 5 nails?

Enrico

Enrico wrote:
> Hi
> 
>> (you havent mentioned the market you are addressing and
>> how critical the board quality is -- are you designing
>> boards that are being used on interplanetary probes?)
> 
> The market is home alarm systems.
> My boards are ordinary 2-layer PCB, nothing special, volumes 10000/
> year.
> 
> 
> PCB makers charge a non recurring fee for bare PCB tests.
> Typical costs range from 500 USD to 1500, that depends on the
> dimensions of the SMD and TH pads that are present on board (fine
> pitches cost more)
> 
> My questions are simple, I guess :-)
> 
> 1) Do PCB makers test the end points of an electrical net, or they
> just test any SMD pad that is attached to the net?

Why don't You ask them?

Rene

Rene <a@b.c> writes:

> Enrico wrote:
>> Hi
>>
>>> (you havent mentioned the market you are addressing and
>>> how critical the board quality is -- are you designing
>>> boards that are being used on interplanetary probes?)
>>
>> The market is home alarm systems.
>> My boards are ordinary 2-layer PCB, nothing special, volumes 10000/
>> year.
>>
>>
>> PCB makers charge a non recurring fee for bare PCB tests.
>> Typical costs range from 500 USD to 1500, that depends on the
>> dimensions of the SMD and TH pads that are present on board (fine
>> pitches cost more)
>>
>> My questions are simple, I guess :-)
>>
>> 1) Do PCB makers test the end points of an electrical net, or they
>> just test any SMD pad that is attached to the net?
>
> Why don't You ask them?

I gather there is a "flying probe" test method that is also used,
presumably for lower volumes.

I usually just tick the "e-test" box on the quote form; they charge an
extra ~0.50 per board plus an extra ~$100 "e-test setup".


-- 

John Devereux

Enrico wrote:
> Hi
> 
>> (you havent mentioned the market you are addressing and
>> how critical the board quality is -- are you designing
>> boards that are being used on interplanetary probes?)
> 
> The market is home alarm systems.
> My boards are ordinary 2-layer PCB, nothing special, volumes 10000/
> year.
> 
> PCB makers charge a non recurring fee for bare PCB tests.
> Typical costs range from 500 USD to 1500, that depends on the
> dimensions of the SMD and TH pads that are present on board (fine
> pitches cost more)

They charge a non-recurring fee to design the test fixture.
They typically then charge a setup charge (for each run of
boards that you make *needing* that fixture) and a *per board*
cost to cover the added testing.

Are you sure you need to burden your product with these
extra costs?  Do you really expect to find any/many problems
that you *wouldn't* solve by REPLACING YOUR VENDOR??

> My questions are simple, I guess :-)
> 
> 1) Do PCB makers test the end points of an electrical net, or they
> just test any SMD pad that is attached to the net?
> 2) Does "Routing option 2" require 2 nails?
> 3) Does "Routing option 1" require 5 nails?

Hi guys,


> Are you sure you need to burden your product with these
> extra costs?  Do you really expect to find any/many problems
> that you *wouldn't* solve by REPLACING YOUR VENDOR??

For medium to high volume PCB productions is mandatory have the vendor
to test EACH pcb after production.


> I usually just tick the "e-test" box on the quote form; they charge an
> extra ~0.50 per board plus an extra ~$100 "e-test setup".

Less or more, those are the costs.


I talked to my vendor and he explained me how the things are. I
learned a couple of very interesting things about bare board tests.
I'm writing a PDF document and by the end of the week I will put it
somewhere on line.

Enrico