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July 2007

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Subject:
From:
John Burke <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, John Burke <[log in to unmask]>
Date:
Thu, 5 Jul 2007 15:30:40 -0700
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Ohm y gosh,

Dewey seems to have had a sense of humor extraction. That is what comes from
having to work from ohm with a Ducati sat in the garage crying out "ride
me"........8-)


John

 
 
John Burke
 
(408) 515 4992

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Whittaker, Dewey (EHCOE)
Sent: Thursday, July 05, 2007 2:49 PM
To: [log in to unmask]
Subject: Re: [TN] Soldermask Thickness

Masking my inhibitions and my humor not withstanding, I will not lecture
on the fallacies of relying on the insulating properties of the Solder
Mask to achieve your as designed minimum dielectric spacing
requirements. However some of the reasons are as follows:

*         Per IPC-6012B, solder resist(mask)thickness is not measured
unless specified in the procurement documentation

*         Per IPC-6012B, if thickness measurement is required it shall
be of the microsection of parallel conductors on the E coupon

*         Per IPC-SM-840D, if a specific thickness is required it shall
be AABUS

*         Per IPC-SM-840D, if a specific breakdown voltage is required
or allowed it shall be AABUS

*         Per IPC-SM-840D, the PB Fabricator shall confirm that solder
mask material shall meet or exceed the minimum value of 500 VDC per
0.001 in. of thickness when tested in accordance withIPC-TM-650, Method
2.5.6.1. 

*         Per IPC-SM-840D, the PB Fabricator shall confirm that any
thickness of solder mask shall meet an absolute minimum breakdown
voltage of 500 VDC.

*         Per your own comments and knowing nothing else, the PB was
tested to meet 500 VDC minimum and you tested at 1200 volts.

 

If after your verification that the proper thickness was
specified/achieved per bullet two and you had proper design spacing's,
you are left with the following:

*         Improper cure of the solder mask

*         Improper registration 

*         Loss of adhesion due to contamination or application

*         Contamination of the substrate prior to application

*         Reduced SIR values due to improper cleaning/application

*         Electrical migration paths formed due to improper
cleaning/application(especially if failure was after exposure to
humidity)

 

I know it's revolting that I've lost my capacitance for humor. It must
be that I am working from ohm.

Dewey

 

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Hogg, Blair K.
Sent: Thursday, July 05, 2007 8:37 AM
To: [log in to unmask]
Subject: [TN] Soldermask Thickness

 

We switched PC board suppliers for one of our products a while back and

have started having hipot issues with components that are connected to

main 110VAC input voltage arcing through the soldermask to tracks

underneath at 1200V hipot voltage. 

 

I'm pretty sure I'll get a few responses that say that we shouldn't be

using the soldermask as an insulator, however, since the change in

supplier seems to coincide with the onset of problems, I've been asked

to evaluate the soldermask thickness as a potential contributor to the

problems. 

 

I would some recommendations on how to measure the thickness of the

soldermask. 

 

Thanks,

 

Blair

 

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