MENTO Closes the DIP Inspection Loop with AOI Mounted Before and After Wave Solder on Through-Hole Lines

Why Through-Hole Assembly Still Needs Optical Inspection

DIP (dual in-line package) assembly is often treated as the "legacy" half of a PCB line: components are inserted, the board crosses a wave solder pot, and the section is considered done. In practice the through-hole stage is where field failures are born — a pin that never entered its hole, a reversed electrolytic capacitor, or a solder hole that looks closed but is not wetted. None of these are visible once the board disappears into final assembly.

MENTO's answer is a line architecture rather than a single machine. The standard DIP configuration runs component insertion machine → DIP AOI before wave solder → wave solder → DIP 2D/3D AOI after wave solder → work station: one closed loop from insertion to touch-up.

Station 1: DIP AOI Before Wave Solder — Catch It While It Is Still Cheap

The pre-wave AOI station sits immediately after the component insertion machine. Its job is to verify that every action the operator (or the inserter) took is correct before irreversible thermal work happens:

• Presence and position — every DIP component is in its designated footprint, seated flat, within tolerance.
• Polarity — diodes, electrolytic capacitors and ICs are oriented correctly; a reversed part caught here costs seconds, a reversed part caught in the field costs a return shipment.
• Pin insertion — all leads are through the holes and none are bent, unextended or short of the pad.
• Collinearity — pin rows are straight enough to enter the wave with a uniform solder fillet.

Boards that fail here are corrected at the insertion station, so the pot only sees assemblies that are mechanically ready for it.

Station 2: Wave Solder

The wave solder process itself is left untouched. MENTO hands the pot a verified board and returns data on what came out of it; flux, preheat and wave parameters stay under the customer's own recipe control.

Station 3: DIP 2D/3D AOI After Wave Solder

Downstream of the pot, a second AOI station inspects the finished joints in 2D and 3D, closing out the classic wave solder defect set:

1. Insufficient soldering and non-wetting
2. Solder bridges between adjacent pins
3. Solder holes and blow holes in the fillet
4. Poor soldering, cold joints and excess solder
5. Missing DIP components and unextended pins
6. Component offset, misplacement and polarity reversal

On the K2005DT online dual-track platform, both rails can run different products at the same time, and the system keeps full-board images for traceability. Nominal specification of the platform:

Station 4: Work Station

The last block in the loop is the rework bench. Because every alarm carries its own image, coordinates and defect class, the operator receives a worklist instead of a suspicion. Boards are repaired once, verified once, and returned to the line.

From Inspection Data to Process Control

An AOI station that only lights up a red box is a sorting machine. MENTO's software layer adds the pieces that make the DIP line measurable:

• Top-10 alarm statistics — the defects that eat the most capacity are ranked in real time, per shift and per product.
• Automatic line stop — alarm counts can be configured to halt upstream equipment when a trend appears, instead of waiting for the end-of-shift report.
• Full-board image export — every PCB image is archived for traceability and customer audits.
• MES/SPC docking — a self-developed MES interface supports both standard and customised data formats.
• Labour-saving mode — one operator can monitor the AOI alarms of several lines through remote data transmission.

At a Glance

Conclusion

The through-hole section does not need more operators; it needs two measurement points placed where defects are still reversible. Inserting AOI before and after the wave solder pot turns a blind thermal process into a closed loop, and turns inspection data into a process-control asset. That is the design logic behind MENTO's DIP line configuration — insertion, verification, soldering, verification again, and a repair station that always knows exactly what it is repairing.