Test points for dense boards

Find a high density connector and bear the cost of adding it to the assembly (assuming you want the ability to test

*any* board, not just prototypes or boards that appear to have problems).

The cost ($ and real estate) of the connector is offset by the surety that it provides the technician ("Is my probe on the *right* pin? Is it making good contact?") and the protection it provides the manufacturer ("oops!") against needless product losses.

Note that the connector need not be overly robust as it will only (?) be used by "skilled professionals" ()

[of course, this isn't always practical for *all* signals so YMMV -- from design to design!]

components on both sides of board and even thinner tracks and smaller vias that are too close to each other. that has made assembly and quality control more difficult. sometimes technician needs to read voltage from a small via and oscilloscope probe or multimeter lead slips and short circuit to points and damages the board significantly.

designing and placing test points in dense boards.

My guys like to put Mictor connectors on busses so they can plug in logic analyzers. I hate that, because thay take up space and playing with LAs wastes time. Nobody needs a LA when they could just think instead.

I like TPs with holes that a scope probe will stand up in, but you are right, they are too big.

Lately we use a TP that's just a tiny copper circle, barely a bump in a trace, with no mask. A tiny etched dot in the middle helps keep a probe from slipping.

We do try to seed our boards with scope ground pads. A 2-56 screw sticking up is nice.

I'm asking for vias on all BGA balls, wherever possible, even if they don't go anywhere.

John

components on both sides of board and even thinner tracks and smaller vias that are too close to each other. that has made assembly and quality control more difficult. sometimes technician needs to read voltage from a small via and oscilloscope probe or multimeter lead slips and short circuit to points and damages the board significantly.

designing and placing test points in dense boards.

You get signal integrity issues with that at higher speeds, unfortunately. Probably not so much of a worry if it's right at the BGA, because the reflection won't be delayed much. Also of course in really big BGAs it's a lot easier to escape all those wires if you don't have a whole bunch of keepouts in there.

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
845-480-2058

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

One often sees pads for a surface-mount connector, where some designer wanted the connector but later production didn't install it.

While that kind of thing is do-able, it's far from ideal: your gizmo will have signals that ought not to be routed too far (or near certain other signals), so there have to be OTHER test points. A field service guy won't have a mating connector and might not appreciate counting over to pin #17 under a microscope.

A hash mark every fifth pad in the silk screen works wonders.

--
You can't have a sense of humor, if you have no sense.

Why don't more engineers think like that? Make things easier for future servicing.

Very good point Mike.

tm

They never have to fix their mistakes. :(

--
You can't have a sense of humor, if you have no sense.

Product development is driven by bean-counters... "repair" is never in their minds, only "replacement". ...Jim Thompson

--
| James E.Thompson, CTO                            |    mens     |
| Analog Innovations, Inc.                         |     et      |
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    |
| Phoenix, Arizona  85048    Skype: Contacts Only  |             |
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  |
| E-mail Icon at http://www.analog-innovations.com |    1962     |
             
I love to cook with wine.     Sometimes I even put it in the food.

Whan are minds for bean counters in the budget? :)

--
You can't have a sense of humor, if you have no sense.

(commenting on engineers...)

Or change a flat, esp. on a pickup. I have a few words to say to the person(s) that designed/approved of the underbed spare rack.

Would you rather have it behind the seat? ;-)

I've driven a pickup for the last 15 years. What bugged me was the jack that came with the truk wouldn't go under the frame when you had a flat, so I had to drive the flat tire up onto the spare, then put a couple 2x12s under the jack to lift it off the spare.

--
You can't have a sense of humor, if you have no sense.

I prefer a square pad, rather than round, or some such. Silkscreen tends to get messy on packed boards.

I don't do it for "repair". I do it for me (debug).

They're always in the budget. They put them there.

You got that right! Mine is so rusted that sucker is never coming out of there.

of

Same thing on the minivan my wife drives. The 'hanger' holding the spare eventually rusted through. (salt and Buffalo winters.) Fortunately it fell off at a parking lot speed bump and not on the highway.

George H.

"Salt"? "Winter"? What's that all about ?:-)

Though maybe I should check my spare on the Frontier... never been used in 11 years ;-) ...Jim Thompson

--
| James E.Thompson, CTO                            |    mens     |
| Analog Innovations, Inc.                         |     et      |
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    |
| Phoenix, Arizona  85048    Skype: Contacts Only  |             |
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  |
| E-mail Icon at http://www.analog-innovations.com |    1962     |
             
I love to cook with wine.     Sometimes I even put it in the food.

h components on both sides of board and even thinner tracks and smaller via= s that are =A0too close to each other. that has made =A0assembly and qualit= y control =A0more difficult. sometimes technician needs to read voltage fro= m a small via and oscilloscope probe or multimeter lead slips and short cir= cuit to points and damages the board significantly.

n designing and placing test points in dense boards.

a removing the mask on a square of ground plane at the edge work quite well too

I've seen that with the right process putting the (micro) via in the pad on BGAs is doable

-Lasse

Jim Thompson wrote in news: snipped-for-privacy@4ax.com:

Your spare is probably flat or too low on air. you might want to carry one of those small 12v air compressors in your trunk,like the MasterFlow MF-1040 I use. plugs into the cig lighter socket. you can get the MF-140 on sale at PepBoys occasionally,for around $21-29. it's not a piece of junk,and it's pretty quiet,not a racketbox like some 12v compressors.

I'd suggest a can of inflator/sealer,but for the hot temps of your clime,I'm not sure the can would not burst on a hot day. (go figure,a can supposed to be kept in the car for emergencies,but can't stand a hot day inside a car....??)

--
Jim Yanik
jyanik
at
localnet
dot com

Probably ;-)

I have one of those, but it's a noisy SOB. I'll check out your suggestion. Thanks!

In the garage I have a real life compressor ;-)

...Jim Thompson

--
| James E.Thompson, CTO                            |    mens     |
| Analog Innovations, Inc.                         |     et      |
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    |
| Phoenix, Arizona  85048    Skype: Contacts Only  |             |
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  |
| E-mail Icon at http://www.analog-innovations.com |    1962     |
             
I love to cook with wine.     Sometimes I even put it in the food.

Likely dry rotted by now.

--
You can't have a sense of humor, if you have no sense.