The electronics Printed Circuit Board industry is evolving as new production technologies become available at low cost. Direct digital printing is making inroads into the traditional photolithography and screen printing processes which have been utilized to manufacture Fast PCB Produce for the last two decades.

Here we shall focus on the utilization of direct digital printing to individualize PCBs just prior to their assembly. The aim would be to print a distinctive mark on each board that can be utilized to identify the board. The mark should be permanent and will probably contain 1D or 2D machine readable codes in addition to alpha numeric characters. The marks must have a 600 DPI (dots per inch) resolution or better due to size constraints on the PCB. We are going to also concentrate on applications which require more that 1,000,000 boards per year. At these volumes automated material handling begins to become extremely important to the overall success from the system.

High volume PCB fabricators use screen printing with thermally cured ink to print the legends that cover each side of the board. Currently digital printing can not print the complete side of any board at a cost that competes with screen printing. Even though many printers, such as the PPS7000, could print all of the nomenclature on the board, here we are going to focus on using digital printing simply to print the individualizing marks.

Several individualizing options exist such as the following:

Preprinted Label Application

Many low volume products get started with labels printed on office equipment and hand put on each Fast PCB Quote just before or after assembly. Because the product volumes ramp the reliability and price of hand applying labels becomes a problem. Automated systems that print and apply labels can be found. (see this site ) Because of PCB space constraints these systems must place labels very accurately, a large problem for most label application systems. The labels are not permanent. At high volumes the labels are more expensive than other marking methods.

Advantages

* Low Initial Cost

* High Contrast Mark

Disadvantages

* Not Permanent

* Higher Incremental Cost

* Difficult to Change Label Size On The Fly

* Mechanical Complexity For Automated Application

Solvent Based Continuous Ink Jet Digital Printing. Continuous ink-jet technology has been adapted to mark on many industrial products including PCBs. Using these systems a continuous stream of ink droplets is steered towards the desired location using electromagnetic fields. Solvent based inks produce permanent marks on porous surfaces. The marks are less permanent on non-porous surfaces where smearing may be a problem for the short period of time its takes to dry.

Advantages

* Competitive Incremental Cost

* High Contrast Mark

* Many Colors Available

Disadvantages

* Complex Ink Viscosity Process Can Be A Challenge To Regulate

* High Definition (Greater Than 300 DPI) Challenging To Achieve?

* Solvents May Be Released Into Atmosphere, Most Companies Seeking To Reduce Solvent Issues

* Mark Not Resistant To Some Cleaning Solvents

Laser Ablated Ink Patches – Many industries use lasers to engrave marks onto many different parts. Lasers have been utilized to engrave marks onto PC boards with limited success as a result of lack of contrast from the resulting mark. A newer approach is to get the circuit boards printed with ink patches, the ink patch will be selectively removed (ablated) from the laser creating the mark to get printed. (see here ) PPSI has the capabilities to develop a laser based marking system.

Advantages

* Competitive Incremental Cost

* High Contrast Mark If Ink Patch Can Be Used

* Very Fine, Highly Reliable Marks Available With Laser Galvo Head

Disadvantages

* High Initial Cost

* Requires Preprinted Ink Patch

* Even At Low Power Laser heat May Damage (by Fracture) Traces, Causing Intermittent Reliability Problems

* Particle Generation May Require A Cleaning Step

Piezoelectric Drop At Will Digital Printing, Solvent Based Ink. For any concise description of drop at will digital printing see here [http://www.aellora.com/documents/whatisdodij.pdf]. For me this alternative represents a little improvement over option 2.

Advantages

* Competitive Incremental Cost

* High Contrast Mark

* Many Colors Available

* Easier Process To Regulate Than Continuous Ink Jet

Disadvantages

* Standoff Distance less Than 2mm, Ideal For Unpopulated Boards Only

* Solvents May Be Released Into Atmosphere, Many Companies Trying To Reduce Solvent Emissions

* Mark Not Resistant To Some Cleaning Solvents

Piezoelectric Drop On Demand Digital Printing, Thermally Cured Ink. A startup company in Israel “Printar” has introduced a printer geared towards low volume, fast turn PCB fabricators who require to reduce the cost and lead time associated with small lot screen printing. Interesting could be the thermally cured ink that reportedly has better adhesion capability than other ink systems.

Advantages

* Good Ink Adhesion ?

Disadvantages

* Requires Large Oven For 350-400 deg F Heat Cure

* Does Not Include High Volume Material Handling

Piezoelectric Drop When Needed Digital Printing, UV Cured Ink. Markem Corporation has created an ink/print head system ( the Model 4000, see here ) that several OEMs and integrators are utilizing to print on PCBs. The device uses an ink that is less viscous at high temperature and almost solid at room temperature. The print head operates at 68 deg C, the ink drops cool once they contact the PCB becoming almost solid. This enables the program to print fine detail on PCBs without ink running or smearing. When in contact with UV light the ink undergoes a chemical reaction transforming into a solid plastic like substance. The cured ink is impervious to common solvents.

Advantages

* Competitive Incremental Cost

* High Contrast With Fine Detail (600 DPI)

* Before Cure, the Ink Can Be Wiped Off And also the Board Reprinted

* After cure, The Ink Can Not Removed Except By Scraping

* High volume Material Handling Available

* Works Well With Inline Inspection (Inspect Before Cure, Cure Only Good Boards)

Disadvantages

* Ink Adhesion Can Be Considered A Problem On Certain Substances

* Requires the PCB Be Clean (No Finger Oils)

* Standoff Distance Less Than 2mm, Ideal For Unpopulated Boards Only

The PPS7000 has been designed to print individualizing marks on Ultrafast PCB Produce using option 6. The system utilizes a SMEMA compatible edge belt conveyor to maneuver PCBs towards the print area where they may be printed and optically inspected. After inspection they may be conveyed for the inline curing station and after that the back of the machine. When being automatically loaded with a board destacker, panels exit qhzwxo system about once every 10 seconds. Each panel usually contains multiple boards that every gets a unique serial number. The overall throughput of the machine is highly dependent on the quantity of boards in each panel. The greater boards in each panel the larger the throughput in boards a minute. A drag and drop WYSIWYG (Everything You See Is Exactly What You Obtain) programming system continues to be developed which allows a brand new panel to become programmed in approximately 5 minutes. An offline programming system is available too.

We have been the only PCB board marking system that creates a lasting (solvent resistant) high contrast mark, incorporates SMEMA compatible high volume material handling and incorporates inline inspection.