SMT is easier to see but the defects are more difficult to discern due to
the size.
Field is view is very different for SMT vs PTH.

PTH defects easily found at AOI are missing, wrong orientation if the top
is looked at.
Many top side fillets are hidden or difficult to see.
Bottom side solder shorts and solder skips show up.
Blow holes, insufficient fill are more difficult.

Depends on lot sizing.
Lots where immediate action can be taken to stop a problem, place the AOI
on the SMT line.
Nothing like 4 magazines of wrong orientation BGA's to ruin your day.

If the SMT line takes up all the AOI time put it in line.

PTH can be visually inspected with a magnifying light.
Again, what is the penalty of a miss?

I had a PCA with 938 2mm pitch pins that was selective soldered.
6,500 units/week.
On 3 seperate occasions over a 2 year period an un-soldered pin escaped to
the field.
Detection went from single visual inspection to double inspection to double
inspection with a microscope and template.
Next was adding AOI if we had stayed open.
No died if this product failed.
Extensive testing occurred after soldering. A pin touching the side of the
PTH would pass test.

As usual it depends.
1. What are the lot sizes?
2. What are the consequences of an escape?
3. AOI takes a lot of care and feeding, do you have the resources available
to program new assemblies, components, suppliers and variations, The
machine is not a set it and forget it. Someone has to analysis the calls.
No escapes, many calls. No calls, some escapes. What is the balance?
4. How many shifts? More help justification but increase need of all shift
technical support. That new Mfg part number, is it because a new source or
site is supplying part or is it wrong? PNP parts on reel mislabled as NPN
parts or did it come from China instead of the Philippines.
5. Looking for presence, polarity and mfg PN? Looking for acceptable solder
joint? 100% or sample inspection?


Larry D


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