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Many industries have precise traceability requirements to which PCB assemblers must adhere. Laser marking offers assemblers a cost-effective alternative.
By José Downes
Figure 1. Laser marking etches important coding information right into the PCB and can withstand the various chemical treatments the board is put through during assembly.
As application-specific components proliferate and printed circuit board (PCB) assemblies grow increasingly complex, the importance of marking boards for identification early in the manufacturing process has become widely recognized. Today, almost all PCBs are marked in some fashion. The automotive, military and medical device industries have precise traceability requirements stipulated by regulatory agencies or de facto industry standards. In addition, virtually all customers of PCB contract manufacturers demand that boards be marked.Marks provide traceability not only for process monitoring and tracking during manufacturing, but also throughout the product life cycle, e.g., for service, maintenance, recalls and warranty management. At a minimum, marking codes identify the supplier and the board type, but they may also contain many other kinds of manufacturer-specific information.
Traditional Marking AlternativesUntil recently, three marking processes were available for PCB assembly manually applied pre-printed labels, automated pick-and-place paper label application systems and direct ink-jet marking. PCB manufacturing is a cost-sensitive operation and labels must add as little cost as possible. It is critical that the marking process does not create production bottlenecks on high-volume lines.
Paper labels and ink-jet marking possess certain characteristics that are problematic in PCB assembly. In many cases, common chemical and thermal processes used in PCB assembly, such as wave soldering and cleaning, affect the mark itself, rendering it useless. This means that most paper labels cannot be applied until late in the manufacturing process, resulting in no traceability in early process stages. Adhesives, liners, static charges and the label's physical thickness can interfere with the PCB's capability to work properly. Ink-jet systems produce volatile compounds as a by-product, creating environmental concerns.
Both methods use board real estate that PCB designers would prefer to apply toward added board functionality. They can also be relatively slow in automated lines, especially for multiup panels, increasing the potential for production line bottlenecks.
Both paper labels and ink jets use consumables that need to be stocked and replaced, with the attendant inventory control requirements for labels, ribbons or inks. The cost per applied PCB label is generally estimated in the range of $0.05 to $0.12 for paper labels and at $0.03 to $0.04 for ink-jet systems.
Laser MarkingRecently, commercial PCB laser marking systems reached the market; they offer some advantages over traditional alternatives (Figure 1). Rather than adding materials to the PCB, laser markers etch a code into the outermost layer of the board. These laser-written codes are durable and permanent, and can withstand virtually all PCB manufacturing processes. PCBs can be marked at the very beginning of the line for complete traceability throughout the process.
Lasers can mark information in extremely small spaces, with laser-readable bar codes, 2-D cell codes, or text written at resolutions as precise as 1.8 μm and positioning accuracy of 0.1 percent. Very densely populated boards can benefit from the laser's ability for precision they feature high throughput, typically 300 characters per second.
Lasers can be programmed to mark anywhere within a working area at 500 x 500 mm, providing flexibility in board layout and handling, excelling on multiup panels.
In addition, lasers use no consumable supplies and require minimum maintenance, for lower inventory and operating costs. The fully amortized cost per PCB label for a laser marking system is approximately $0.01 or less. Fully equipped PCB laser markers are available for under $100,000.
Laser markers are SMEMA-compatible, ensuring easy integration into automated production lines. Both YAG and CO2 lasers are available in a range of power options, to permit the selection of the laser best suited to the particular material to be marked.
Issues to ConsiderThere are several factors that need to be considered to ensure successful implementation of laser marking technology for PCB identification:
- Why is the marking being performed? Are marks to be used for internal identification only, by third parties or customers?
- What range of board sizes will be handled with a single marking system? Where on the board is the available marking area?
- What size marks will be required? Must the marks be readable by humans or will they be exclusively machine-read?
- Do multiboard panels, as well as individual boards, need to be marked?
- What is working well and working poorly in the current marking operation? What does marking cost today?
- What information needs to go on the boards and in what form does it need to be presented? Are text, bar codes, cell codes or some combination needed? Will boards be serialized?
- What throughput is required to avoid bottlenecks? What is the current marking throughput?
- What type of material will marks be placed on? (This is an essential piece of information for selecting the proper laser.)
Like any piece of capital equipment, a laser marking system needs to be cost-justified for use in a particular application on a particular manufacturing line. If a marking solution that delivers flexibility, quality and economy is desired, try running the numbers.
Lasers: Fact or Fiction?Despite the fact that lasers today are as ubiquitous as office printers, several misconceptions remain about this technology, especially concerning PCB marking. Here are a few instances where myths about lasers may overtake reality.
Myth: Lasers require special power sources, cooling and constant adjustment.
Fact: The water-cooled lasers of generations ago did require lots of power and tweaking, but today's air-cooled systems use standard power sources and typically operate for months without adjustment.
Myth: Lasers are maintenance-intensive.
Fact: While older arc-lamp lasers need ongoing recalibration, today's lasers are practically maintenance-free.
Myth: Implementing and operating a laser system is difficult.
Fact: Today's lasers are easy to program and operate, featuring Windows-based operating systems and WYSIWYG graphical user interfaces for high programming productivity. State-of-the-art software makes setups and changeovers a simple matter.
Myth: Lasers need an on-site laser specialist.
Fact: Advances in the field of laser/material interaction now make it easy to specify which types and strengths of lasers are best for a given marking application. There is no need to hire a laser expert to manage the operation. System suppliers provide the level of training necessary for maximum system performance.
Myth: Laser systems are expensive.
Fact: Laser marking offers lower costs per PCB than current alternatives, and new systems arriving on the market are extremely cost-effective for most medium- to high-volume PCB manufacturing lines.