Inspection of Solder on Hidden, Top-side Pins

..."Visual and X-ray inspections are not always enough to ensure the integrity of a board. To make sure that your PCB manufacturer met your requirements, ask for a cross-section analysis. This destructive technique is the best way to verify your PCB internal structure, mostly using a microscope. The test can check for various aspects, such as cracks, voids in solder joints, through-hole filling, etc."...

Regular cross-section analysis is necessary...

Class 3 = High Reliability Electronic Products

https://www.protoexpress.com/blog/ipc-class-2-vs-class-3-different-design-rules/

http://www.circuitnet.com/experts/86649.html

https://blog.jjsmanufacturing.com/ipc-standards-for-acceptability-and-why-they-matter-to-your-pcb-assembly

I don't know what connectors you are using but I wonder if the "inspection holes along the bottom" are actually holes to allow the board wash to drain out.

I agree with what SolarEagle posted but I'll add a possible twist to it. Are you the manufacturer or consumer of the boards? If you are the manufacturer can you adjust your wave machine pressure or have your people adjust after wave manual operations to always fill the barrels to 100% or greater so the fill can be seen? The destructive sampling process SolarEagle posted requires that your process always be consistent enough for the inspected sample to be valid. Adjusting your hole size, wave pressure or manual process to allow 100% visual inspection might be easier than being able to prove that every production unit is accurately represented by the sample unit.

Ok, I'll clarify a couple things. We are a contract manufacturer; we simply build to our customer's design prints. This particular board, we outsourced because of some requirements for processes we don't do in-house. So, we are stuck to inspecting to the drawing requirement of IPC-A-610 class 3. We aren't going to section because that requirement wasn't priced into the job or required by the contract.

And, yes, the holes probably are for cleaning after processing. Even if we did these boards ourselves, one limiting factor is the presence of internal copper planes inside the board that suck up heat and limit the flow of solder. Sure, proper pre-soak would take care of that, but...

The real question is, does anyone know if this is an exception to IPC requirements for vertical fill (sect 7.3.5.1.) when you can't see the interior of the hole?

I think this sort of thing is stipulated in the customer requirements as in we want these solder holes visually inspected ....Short of any attachment of these instructions to the order, leaves the methodology in your hands...you only have to meet reliability requirements of a class 3 component board....and follow all other class 3 requirements...You could of course incorporate Borescope Inspection Cameras.....

http://www.ipc.org/committee/drafts/7-31b_d_610F-draft-Feb2012.pdf

I'm a little rusty on IPC, but sounds like the board fails to be able to be inspected, so seek the customer's feedback. Solution might require board design change to create a plated through hole (inspectable) to verify the joint quality additional to the PTH for the connector mechanical connection.

Been away from that industry for 9 years, so IPC possibly reviewed at least twice in that time.