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June 2011

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Subject:
From:
Don McFarland <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Don McFarland <[log in to unmask]>
Date:
Thu, 16 Jun 2011 12:04:33 -0600
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text/plain (181 lines)
Sure...here are a couple: 

We have had switches fail for mechanical isolation caused by contamination in a dielectric gel that we bought. The particle was about 0.003" and minimum lead spacing on the mostly TH assembly was over 0.100"...no real risk of shorting there. 

We also had a bunch of lot/delivery of relays seize because of FOD (in this case it was corrugate particulate from vendors packaging) that blocked the armature from moving. 

I'm not saying that it is common, but its definitely worth considering this type of failure mode when evaluating acceptability of residual FOD. I know that weve been burned by this and wanted to share it with the group...I know that i have learned a lot of lessons, before issues arose, from the experts that walk the proverbial TechNet halls. 

Don McFarland
Compliance and Training Manager / FSO
Inovar, inc. (3P0G4)



----- Original Message -----
From: "Richard D. Stadem" <[log in to unmask]>
To: "TechNet E-Mail Forum" <[log in to unmask]>, "Don McFarland" <[log in to unmask]>
Sent: Thursday, June 16, 2011 11:38:31 AM
Subject: RE: [TN] PCBA Inspection for Solder Balls/Splashes

Can you provide an example of this? I cannot think of any relay or switch or any other component where this could happen. Motors I can understand, if there was a power supply or motor control mounted nearby. Common design practice typically puts those type of devices inside an enclosure to protect it from the environment and from the motor itself.

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Don McFarland
Sent: Thursday, June 16, 2011 12:20 PM
To: [log in to unmask]
Subject: Re: [TN] PCBA Inspection for Solder Balls/Splashes

Let's remember that dislodged and loose FOD can also have mechanical concern as well as the shorting/electrical concerns. Some components (e.g. motors, switches, relays, etc) are potentially seriously impacted by these small solder balls, although they may be so small that they wont cause an short/electrical performance anomaly. If youre going to go this route, I would caution you to consider these potential failure modes in your assessment. 

Don McFarland
Compliance and Training Manager / FSO
Inovar, inc. (3P0G4)



----- Original Message -----
From: "Reuven Rokah" <[log in to unmask]>
To: [log in to unmask]
Sent: Thursday, June 16, 2011 11:09:26 AM
Subject: Re: [TN] PCBA Inspection for Solder Balls/Splashes

You should check the size and quantity of the particles and simulate the
case of such loose part can short conductive traces, open component (such as
relays). if the is no option to cause a short during the simulation, I think
you can approve it.  In parallel you should take care for improving the
process and implement corrective actions steps to eliminate those particles.

Reuven.

On Thu, Jun 16, 2011 at 5:24 PM, Forrester, Michael (H USA) <
[log in to unmask]> wrote:

> I have a question about solder balls/splashes on PCBAs.  in IPC-A-610E
> section 5.2.7.1 it mentions that solder balls and "fines" that are NOT
> encapsulated in flux is a defect.
> Section 5.2.7.3 mentions that the inspection for said solder anomalies
> shall be done with NO magnification.  We have an SMT assembly that is
> manufactured with water soluble flux and has two SMT parts hand soldered
> to the board with No-Clean.  In reviewing the rework under
> magnification, we discovered solder slivers entrapped in the No-Clean
> flux that did not violate the minimal electrical clearance.  So far so
> good.  I have several assemblies where there are unmelted solder balls
> from the paste and solder slivers (4-5 mils) spread all over the PCB NOT
> entrapped in any flux.  I can not see them without magnification, so
> does that mean that they pass the IPC-A-610E specification?  In thinking
> about this, in theory, once the board is put into service all of the
> solder anomalies, not entrapped in flux, could shake loose, converge and
> create a short?  So hence my confusion between section 5.2.7.1 and
> 5.2.7.3.  Any thoughts would be appreciated.  Thank you.
>
> Best Regards,
>
> Michael Forrester
> Sr. Product Engineer
> CSMTPE
>
> Siemens Healthcare Diagnostics
> 101 Silvermine Rd.
> Brookfield, CT  06804
> PH: (203) 740-6452
>
>
>
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-- 

Best Regards,

*Reuven Rokah*

Mobile: 972-52-60-120-18
Tele-fax: 97239360688
<http://www.rokah-technologies.com/>[log in to unmask]
[log in to unmask]
www.rokah-technologies.com

**


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