Cheer up, Andrew. 

Assume all solder mask is a minimum of .005" thick.

Nobody has to measure.

Nearly all minimum electrical clearances (almost always noted on the fabrication drawing) are at least .005". For high voltage applications, it should definitely be defined on the fab drawing.

So, based on a halfway decent X-ray machine image, consider the soldermask to be non-existent.  Anything seen within the minimum electrical clearance that is not down below the top and bottom layers, is a defect.

Any solderballs from a straight-down view need to be a minimum of .005" away from any pad, electrical trace, or conductor seen on the first layer down, unless it is a high-voltage application. Don't know? Ask the customer.

I have never, ever heard of an EMS that did not have the fab drawing of the PWB to determine what is on the top and bottom layers.

How do you order a stencil without the fab drawing?

I am sure your design office would provide that info. If not, contact the PWB fabricator; they would not be able to manufacture the PWB without it!

Rikard Odin Stadheim



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From: TechNet <[log in to unmask]> On Behalf Of Andrew Hoey

Sent: Monday, September 14, 2020 9:21 AM

To: [log in to unmask]

Subject: Re: [TN] Solderballs



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The difficulty of not knowing voltages is because we are a subcontractor, so need to wait for customers to supply that information, and when we have had responses there are areas of the board operating at different voltages, so translating and mapping this to operators/ inspectors can be difficult. We're then asking people to measure down to 0.13mm at 20x to 40x magnification in some cases (0-15V category A6 applies to some of our boards). 



Then that is okay and a measurable amount if we are only regarding the surface of the board. But different applications of masking can leave varying thicknesses, so is it actually impossible to know the masking thickness in each specific area below a solderball (unless you microsection it) - regardless, if masking isn't specified as an insulator surely they ally violate MEC?



I know i'm getting hypothetical here but it is now becoming a niggle at the back of my mind, unanswered questions make me sad!