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Driving Innovation: Traceability in PCB Production

Traceability across the entire printed circuit board production process is an increasingly important topic among established manufacturers and companies considering new PCB facilities. The reasons are apparent:

• Automatic loading of part programs
• Connection with MES systems and collection of production data
• Compliance with Industry 4.0 requirements

While basic solutions, such as manual barcode scanning, exist, they’re not the focus here. Customers are seeking a traceability function integrated directly into the production equipment. However, the complex nature of PCB fabrication, which involves mechanical, optical, and chemical processes, presents certain challenges. This article explores the traceability opportunities and limitations within the process steps of Schmoll machines.

Inner Layer Exposure
Customers aiming for full traceability often prioritize inline processes that minimize operator interaction, starting with dry film pretreatment and continuing through to resist stripping at the end of the DES (develop, etch, strip) line. In these cases, it’s easy to implement inner layer traceability because:

• A data matrix code is laser-marked at the entrance of the line
• The direct imaging machine exposes it directly

This allows traceability to be built into the process from the earliest stages.

Since codes are typically placed on the technological frame, it’s important to ensure they remain undamaged during handling—or to include a backup code as a precaution.

Inner Layers Before Lamination
There are various methods for inner layer alignment. If the manufacturer uses a post-etch punch system, the machine should be equipped with a data-matrix code reader. The customer must then manage the traceability during the layup stage.

X-ray and Through/Blind-hole Drilling
Things become more complex after lamination. Copper covers the top and bottom surfaces, making it impossible for standard scanners to read through the copper. However, it is still possible to use an X-ray source to read a data-matrix code on an inner layer. From this, the machine can load the correct part program, locate fiducials, and link to the MES system.

Following X-ray, should the process create a new code using a laser, via drilling, or through another method? If so, which code works best? The decision must take several factors into account, including:

• The code must withstand subsequent processes, such as scrubbing and plating
• It must remain readable at later stages (e.g., direct imaging)

If each drilling station reads codes individually, the manufacturer must equip every station with a scanner and ensure it operates independently, which significantly raises the cost. In that case, stack drilling would not be possible, affecting productivity for boards that do not require optical alignment

Unique Serialization Path
If unique serialization is required, the most stable method is to drill the data-matrix code during the X-ray stage. However, this affects throughput. Code drilling slows the X-ray process as it needs additional time for the code drilling and can create a production bottleneck.

Alternative: Job-based Traceability
Another option is using job-level traceability rather than full serialization. In this model, the sequence is:

• A laser marker at the X-ray stage creates a code without slowing down processing
• The code is read at station 1 of the drilling machine to load the job
• All stations then drill into each board:

1. A job-specific data-matrix code
2. Date and time of drilling
3. Machine number
4. Station number (1–6)
5. Operator ID

While this approach doesn't provide full traceability, it strikes a balance between cost and process visibility. It provides some information to track production history without creating a bottleneck at the X-ray stage, since we drill the job code at the drilling machine.

Which approach is right for you? It depends on your vision of the factory and desired level of traceability.

Outer Layer and Solder Mask Exposure
Once a drilled data-matrix code exists, be it a unique identifier or a job code, it will probably survive subsequent processes. This makes it easily readable by the direct imaging system at the outer layer or solder mask exposure stage.

Summary
Full traceability with unique serialization in PCB production is possible, but is it always practical or necessary? The answer depends on the specific needs, cost considerations, and production volume of each factory.

This column originally appeared in the May 2025 issue of PCB007 Magazine.