Jack,
Probes can be moved after the fixture is made so long as they are moved at
least 50mils from
their previous position (or whatever distance your test vendor says). They
need to be far enough away for
manual drilling for hole wall thickness issues.
As far as using the via, can you just open the mask up and use a castle /
tulip type probe?
Ken
_____________________________________
Kenneth J. Wood
Saturn PCB Design, Inc.
www.saturnpcb.com
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Jack Olson
Sent: Wednesday, August 12, 2009 2:03 PM
To: [log in to unmask]
Subject: Re: [TN] ICT and SolderMask
(Sorry I got busy and set this conversation aside)
I don't have much experience on the subject of ICT, but according to the
SMTA Testability Guidelines TP-101C, vias are perfectly acceptable ICT test
point sites as long as the pad diameter is large enough.
The only warning I can find is in Guideline #P-7 where it states:
*
-=-=-=-
GUIDELINE #P-7 Select Appropriate Test Via Drill Sizes for Your Application.
*The drill holes size of test vias has a significant impact on test probe
contact repeatability. It is intended for the test probe to strike either
the solder that fills the via hole during processing or the outer edge of
the empty via barrel.
If the via drill size is too large, the test probe may enter the hole and
hit contaminates before the sides of the test probe, which results in
contact problems. Typically a 0.012 in. (0.305 mm) drill is acceptable with
100, 75, and 50 mil (2.54 mm, 1.91 mm, and 1.27 mm) test probes. Using
larger drill sizes may eliminate the use of some of the smaller diameter
test probes.
Guideline #P-19 only reasserts the point that vias can be used:
*GUIDELINE #P-19 Probe Test Pads or Vias, Not Components or Component Leads*
.
Contact pressure can cause an open or make a cold solder joint appear good.
Component mounting variations may also result in missing the target and
possibly probe glancing, causing fixture induced shorts and probe damage.
-=-=-=-
Anyway, I guess the real intent of my question was directed more towards
what happens down on the production floor when the fixture is used for the
first time.
Are any of you aware of the technicians wanting to move probes during a
"debug" phase?
thanks
Jack
On Mon, Jul 13, 2009 at 10:52 AM, Rex Waygood
<[log in to unmask]>wrote:
> I'm interested as to what type of probe you use to make good contact and
> ensure you have no risk of damaging the via?
> We avoid probing vias at all costs.
> The via is a potential reliability concern on a pcb and hitting it
> repeatedly with a steel probe doesn't seem sensible.
> Regards
> Rex
>
> Rex Waygood
> Technical Manager
>
> Hansatech EMS provides value manufacturing through engineering and
> quality
>
> Hansatech EMS Limited
> Benson Road
> Nuffield Industrial Estate
> Poole
>
>
>
>
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of Jack Olson
> Sent: 10 July 2009 18:20
> To: [log in to unmask]
> Subject: [TN] ICT and SolderMask
>
> I'm wading into deeper water these days...
>
> (As a circuit board designer,)
> We have vias that can be used as test points that are 40mil pads with
> 13mil holes. Normally we would like mask to cover most of the pad but
> not the hole, so we have an 18mil aperture on the mask layer.
> Whenever these vias are USED as test points, we have to open up the mask
> and leave them fully exposed.
>
> The problem is, no matter how hard we try to generate test point data,
> during test fixture development they end up inserting a few more, moving
> them around, etc. which means we either have to modify the mask or leave
> ALL of them exposed. to minimize the possibility of solder shorts, we
> are discussing now to modify the mask instead of leaving them all open,
> preferably without having to change the board revision.
>
> Has anyone else had to deal with this situation?
>
> I would be interested to know if you are generating test point data, Is
> it really good enough?
> Or,
> Are they modifying it in production?
> If so, do they make an effort to get the TP changes back to you?
>
> the man with the mask,
> Jack
>
>
>
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