Non Stick on Pad
Non-stick on pad (NSOP) is a wire-bonding failure where the wire never actually metallurgically welds to the bond pad at all — it just sits there, mechanically touching the metal without atoms from the wire and the pad ever diffusing together, so the bond looks present until something as small as a light touch or a thermal cycle lifts it right off. It is the mirror image of pad cratering: cratering comes from too much bonding energy cracking the dielectric underneath a bond that formed fine, while NSOP comes from the bond never truly forming in the first place, usually because something stood between the wire and the pad the whole time.
A pad's native oxide is thin enough to ignore and thick enough to ruin a bond. Aluminum bond pads form a few nanometers of native aluminum oxide on exposure to air almost instantly, and that oxide is an electrical insulator and a mechanical barrier that the bonder's ultrasonic energy has to physically scrub through before the underlying aluminum can touch the wire and weld — anything that makes that oxide thicker than normal, or anything else sitting on the pad surface such as process residue, moisture, or an organic film, raises the odds that the scrubbing never breaks all the way through and the bond stays non-stick across some or all of its footprint.
Detection relies on exactly the same destructive tests that catch pad cratering, reading the opposite signature. A ball shear or wire pull test on a good weld fails by breaking the wire itself or lifting a sound chunk of the pad metal with it, while an NSOP bond fails by lifting cleanly off the pad with little to no force and no metal transferred at all — packaging houses read that failure mode, not just the force number, because a weak-but-real bond and a non-stick bond can sometimes pull at a similar force while failing for completely different reasons.
Prevention lives upstream of the bonder, in how the pad surface was prepared and stored. Fabs and packaging houses use plasma cleaning immediately before bonding specifically to strip the native oxide and any organic residue off the pad right before the wire ever touches it, and bond pads that sit too long between that clean step and the actual bonding operation can re-oxidize enough to raise NSOP risk again — which is why bonding is typically scheduled close to the surface-prep step rather than treated as an independent, schedule-flexible operation.
Read NSOP through a *barrier-not-broken* lens rather than a *weak-bond* lens — the wire and the pad were never actually joined, so no amount of post-bond handling care saves a part that failed this way, and the only real fix is making sure the pad surface is clean at the moment the bonder's energy is supposed to break through it.