Others are densely populated with little or no room for product information. PCBs destined for consumer products are extremely cost-sensitive, and markings, if any, must not add additional cost to the product. On the other hand, PCBs in large ticket items such as automotive products, military electronics and medical devices may face strict marking and traceability requirements imposed by government and regulatory agencies.

PCB Identification Requirements

As PCB manufacturing continues to evolve, identifying PCBs during assembly increases in importance. Factors to be considered include.

Addressing Mandatory PCB Identification Requirements. PCBs are generally marked with two mandatory data fields: supplier identification code and item identification code. The former provides a way to identify the supplier of the product and the latter a way to identify the product itself. Optional data fields may include a traceability code and a country of origin.

Compliance with PCB Identification Standards, Specifically: ANSI MH10.8.3 M/ISO 5434, ANSI/EIA 706 and EIA PN 3497. ANSI/EIA 706 describes the requirements for using formatted, 2-D, machine-readable symbols for the marking of electronic components or first-level assemblies. Bare boards are considered components, while populated PCBs or PCMCIA cards are viewed as first-level assemblies. EIA PN 3497 provides a means for products to be marked and read in fixture or handheld scanning environments at any manufacturer’s facility. The codes can then be read by customers purchasing products for subsequent manufacturing operations, or by the end user.

Facilitating High Volume PCB Processing and Assembly. The marking process should not be the bottleneck or throughout-pacing operation. It must be able to identify single and multi-up boards, accommodate varying board widths, provide marking placement within the X and Y plane, and comply with SMEMA machine interface standards.

Promoting Just-in-time Manufacturing and Reducing Work in Process Inventories. Setup and part changeover times must be minimal. Downtime associated with operation setup, equipment malfunction and the replacement of consumables negatively influences process cycle time.

Assisting with Field Service, Warranty Repairs and Identifying Non-repairable Components. The ability to uniquely identify each PCB will assist PCB manufacturers with inventory control, facilitate automatic setup of downstream processing equipment and assist with warranty repairs or customer returns.

Reducing Waste in Terms of Material Handling, Rework and Repair Cost, Improper Material Usage and Material Scrap. The marking process is typically viewed as a non value-added operation. Inefficiencies affect product-marking costs and can substantially hinder PCB processing throughput.

Compliance to ISO 9001 requires identification of the product during all stages of production, including delivery and installation, where required. It would be advantageous to PCB manufacturers if designers were to design the product identification system to meet product traceability requirements. The product identification should provide PCB manufacturers with the ability to correctly obtain materials, components and processing information specific to the unique PCB.

Marking Process Flexibility

To address PCB marking requirements, manufacturers have relied on four methods of product identification; manually applying preprinted labels; direct inkjet marking; laser etching; and automatic pick-and-place label application systems. Each process, or technology, offers manufacturers a different level of flexibility. Flexibility is important in PCB manufacturing because marking requirements change frequently. Today, a barcode is required. Tomorrow, the barcode may be replaced with a 2-D code Symbology (see table).

Label Use - The Hidden Costs

Ideally, PCBs should be identified at the beginning of the manufacturing process and read at each subsequent operation. The most widely used method has been manually applying preprinted labels. With PCB manufacturers moving towards inline automated processes, automatic pick-and-place label systems have emerged. These systems automatically dispense and position preprinted or print-on-demand labels onto desired areas of PCBs.

The use of labels on PCBs has many drawbacks. First, the cost of labels varies based on the label stock and ribbon requirements. The average cost of a 1.00 x 0.25” preprinted polyester label is $0.03 per label. Individual label costs increase as label stock requirements change from the low cost polyester label to the high cost ESD polyimide label. It is not uncommon for label cost to exceed $0.10 per label for ESD Kapton labels.

Labels require inventory control of label stock and ribbons. Selecting the correct label requires a review of several considerations: physical space available, surface appearance, adhesive type, attachment method, environmental concerns and ESD. Another concern is that labels are a capacitor. A standard polyimide label can have a charge of > 5,000V/cm.

Excessive label thickness can cause problems during solder paste printing. Because of this, many manufacturers are implementing product identification later in the PCB assembly process. This delay in labeling can hamper product traceability. Ideally, PCBs should be identified at the beginning of the manufacturing process, with each subsequent operation using the machine-readable information from the product marking. The benefits to marking the product at the beginning of the process include:

Inkjet Technology - A Direct Product Marking Process

Industrial inkjet and laser product marking processes offer alternatives to the use of labels. Only laser etching and inkjet marking of PCB provide manufacturers direct product marking (DPM). DPM offers a variety of benefits including counterfeit and theft prevention, process and quality control, traceability and cost reduction. Ultimately, the cost per mark of DPM systems is far less than label application systems.

The PCB industry is familiar with laser marking technology. However, the use of inkjet technology is relatively new. Inkjet marking offers PCB manufacturers some advantages over laser technology. Laser marking is permanent immediately after etching. Inkjet becomes permanent after exposure to wave solder or curing operation. The use of inkjet eliminates the need for the Hysol yellow patch that is required for a good laser mark. Material cost savings have been afforded in switching from Hysol ink to a lower cost white patch. An automatic PCB inkjet-based marking system typically requires less physical space than its laser counterpart.

Inkjet-based PCB marking systems are also better able to address print contrast requirements. This is especially important when printing machine-readable codes.

Automated inkjet marking systems offer PCB manufacturers all of the benefits of labels without the liner, adhesive and label thickness issues. Inkjet systems require no contact with the surface of the PCB during marking. In fact, the ideal marking height is 0.125 to 0.375” above the intended marking surface. There are existing applications where the inkjet head is traveling 0.500” above the PCB.

Inkjet technology has been around for years. The first industrial inkjet coder was developed and marketed in 1967 by Videojet Systems International. At that time the beverage industry was seeking an alternative technology that could provide product identification on curved-bottom aluminum cans. A similar paradigm has occurred with the PCB industry. The availability of inks that dry on contact and that are solvent and alcohol wipe resistant, combined with the advent of higher resolution inkjet nozzle technology, enables PCB manufacturers to include inkjet systems as a viable product marking process.

In 1994, Videojet Systems International introduced a high resolution printer capable of printing alphanumeric text as small as 0.35” tall or 3 point. Another improvement was the elimination of the “dot matrix” character appearance. New inks were developed for the high resolution inkjet printing. Today, there are inks capable of meeting the marking permanency requirements of Mil-Std 202, Method 215, as well as Mil-Std-130.

To satisfy the needs of the PCB industry, inkjet inks are available meeting the following criteria:

One major advancement in industrial inkjet printers has been the design and integration of closed-loop ink viscosity management systems. Today’s inkjet printers automatically add ink or makeup fluid to their internal ink module to maintain the proper ink viscosity. In addition, an autoflush feature has been added to inkjet printers to eliminate the potential of ink drying within the ink return line. The autoflush feature also minimizes the frequency of head cleaning. The internal hydraulic systems virtually eliminate hazardous waste disposal. Because the printers consume all of the ink in the system, there is none to dispose. A low evaporation fluid control system reduces odors and fumes emitted into the air. An external volatile organic compound (VOC) emission elimination device is available that destroys more than 96 percent of VOCs emitted from the printer’s exhaust into the air of manufacturing facility.

Automated PCB marking systems featuring inkjet technology offer all of the advantages of labels without the cost of labels and ribbons. The average cost of an inkjet printed product identification mark is less than $0.017 per mark. A fully automated board marking system, complete with SMEMA conveyor, inkjet printer, integrated barcode or 2-D code scanner and host interface can be found for less than $100,000. Automated PCB marking systems can be installed offline, thereby servicing multiple production lines, or in-line for high throughput. A typical four-up PCMCIA PCB can be printed and barcode verified in all four positions in fewer than 10 seconds.