Choosing a PCB Printing Solution
 by: Chuck Raymond


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 that have been used to manufacture PCB for the last twenty years.

Here we will focus on the use of direct digital printing to individualize PCBs just prior to their assembly. The goal is to print a unique mark on each board that can be used to identify the board. The mark must be permanent and will probably contain 1D or 2D machine readable codes along with alpha numeric characters. The marks must have a 600 DPI (dots per inch) resolution or better due to size constraints on the PCB. We will also focus on applications that require more that 1,000,000 boards per year. At these volumes automated material handling starts to become very important to the overall success of the system.

High volume PCB fabricators use screen printing with thermally cured ink to print the legends that cover each side of the board. At this time digital printing can not print the whole side of a board at a price that competes with screen printing. Even though many printers, including the PPS7000, could print all the nomenclature on the board, here we will focus on using digital printing only to print the individualizing marks.

Several individualizing options exist including the following:

Preprinted Label Application

Many low volume products start with labels printed on office equipment and hand applied to each PCB prior to or after assembly. As the product volumes ramp the reliability and cost of hand applying labels becomes a problem. Automated systems that print and apply labels are available. (see this site ) Because of PCB space constraints these systems must place labels very accurately, a big problem for many 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. With these systems a continuous stream of ink droplets is steered to the desired location using electromagnetic fields (see here ). 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 time its takes to dry.

Advantages

Competitive Incremental Cost
High Contrast Mark
Many Colors Available

Disadvantages

Complex Ink Viscosity Process Can Be Difficult To Control
High Resolution (Greater Than 300 DPI) Difficult To Achieve?
Solvents May Be Released Into Atmosphere, Many Companies Trying To Reduce Solvent Issues
Mark Not Resistant To Some Cleaning Solvents


Laser Ablated Ink Patches

Many industries use lasers to engrave marks onto a variety of parts. Lasers have been used to engrave marks onto PC boards with limited success due to the lack of contrast of the resulting mark. A newer approach is to have the circuit boards printed with ink patches, the ink patch is then selectively removed (ablated) by the laser creating the mark to be printed. (see here ) PPSI has the capabilities to develop a laser based marking system.

Advantages

Competitive Incremental Cost
High Contrast Mark If Ink Patch Is 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 On Demand Digital Printing, Solvent Based Ink
For a concise description of drop on demand digital printing see here. In my opinion this option represents a slight improvement over option 2.

Advantages

Competitive Incremental Cost
High Contrast Mark
Many Colors Available
Easier Process To Control Than Continuous Ink Jet

Disadvantages

Standoff Distance less Than 2mm, Suitable 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” (see here) has introduced a printer targeted at low volume, fast turn PCB fabricators who need to reduce the cost and lead time associated with small lot screen printing. Interesting is their 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 On Demand Digital Printing, UV Cured Ink

Markem Corporation has developed an ink/print head system ( the Model 4000, see here ) that several OEMs and integrators are using to print on PCBs. The system 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 when they contact the PCB becoming almost solid. This allows the system to print fine detail on PCBs without ink running or smearing. When exposed to UV light the ink undergoes a chemical reaction becoming 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 the Board Reprinted
After cure, The Ink Can Not Be 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 A Problem On Certain Substances
Requires the PCB Be Clean (No Finger Oils)
Standoff Distance Less Than 2mm, Suitable For Unpopulated Boards Only

The PPS 7000

The PPS7000 has been designed to print individualizing marks on PCBs using option 6. The system uses a SMEMA compatible edge belt conveyor to move PCBs to the print area where they are printed and optically inspected. After inspection they are conveyed to the inline curing station and then out the back of the machine. When being automatically loaded by a board destacker, panels exit the system about once every 10 seconds. Each panel usually contains multiple boards that each receives a unique serial number. The overall throughput of the machine is highly dependant on the number of boards in each panel. The more boards in each panel the higher the throughput in boards per minute. A drag and drop WYSIWYG (What You See Is What You Get) programming system has been developed that allows a new panel to be programmed in approximately 5 minutes. An offline programming system is also available.

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

Product Brochure

Next Steps

If the PPS7000 looks like it may meet your requirements the next step is to print samples for you in order to verify that the ink will adhere well to your substrates.

Please contact us to arrange for printing samples.

Our address is:
Prototype and Production Systems Inc.
13000 Hwy 55
Plymouth, MN 55441
Phone: 763 557 9348
Fax: 800 483 2208
Email: [email protected]
Site: http://www.prototypesys.com

About The Author
Chuck Raymond is the president of Prototype & Production Systems, Inc. He has 25 years experience in the automation and machine vision world and has built multiple PCB and generic printers in the past.

© 2006 by Prototype & Production Systems, Inc. Free for unlimited distribution as long as this copyright notice and link to http://www.prototypesys.com are in place.