In this column, Orbotech West DI expert Rick Jackson provides a guide detailing which issues should be considered when choosing a new DI system.
Key Considerations for Your Next Direct Imaging System
by Rick Jackson
Trends in IoT, 5G, autonomous vehicles, mobile devices, and robotics are increasing the demand for flex and rigid-flex PCBs. The need for high-density electronics, thinner layers, and finer lines is growing, as is the need for direct imaging (DI) or laser direct imaging (LDI) systems that ensure these requirements are met. As your PCB manufacturing company considers a new DI system, here are some key considerations to keep in mind.
Ability to Handle High Depth of Focus
The essential problem is that most PCBs are not flat. There’s variability in board thickness, especially for flex or rigid-flex designs that have multiple levels or varying degrees of board elevations that make exposure more difficult. These require a high depth of focus (DOF) for the DI. Most DI systems, though, are limited in their DOF. As thickness variations increase to 50–100 microns or more, these DI systems become unusable. It’s very important to select a DI that can handle the depth of focus needed for the products you’re producing.
Advanced Scaling Capabilities and Fast Target Acquisition
The registration criteria are getting smaller and tighter on today’s PCBs. The printed pattern must match the physical image. If a conventional registration mechanism with X/Y scaling is used, the registration is acceptable; however, this will not account for board deviations due to the process. This is where non-linear or advanced linear scaling comes into play, as a critical factor for advanced PCB manufacturing.
If a board has a trapezoid shape, for example, you need a scaling system that can handle the unusual dimensions. Most DI systems will not provide good registration for this kind of shape, so those with non-linear or advanced linear scaling are recommended to provide the most accurate registration. In another example, DIs may need to scale and register to individual boards or arrays. For some board designs, this is required to achieve the necessary registration results.
Fast target acquisition is a related capability to consider. If measurement time is 0.5 seconds per target, then 50 PCBs with four targets each calculates to 100 seconds to complete the measurements. And this does not include the printing time for each board. As we know, time is money in PCB manufacturing, so it’s important to look for a DI system that can reduce target acquisition time.
Measuring multiple targets at a high rate of speed—fast target acquisition—is another critical factor in advanced PCB manufacturing. With an Orbotech DI system, for example, the measurement time is only 3–5 seconds for 50 PCBs, and it can print simultaneously due to the dual-table design, which is a unique feature.
Traceability, Industry 4.0, and Automation
In the U.S., traceability is quickly becoming an important factor because Industry 4.0 is gaining interest. The biggest concern for PCB manufacturers is the quantity of information that’s needed on the boards. It’s a real estate issue. An advanced system is needed that can utilize compound stamps that occupy a very small space on the boards that provide all information required for traceability. Typical DI systems can create standard traceability stamps in a 2D barcode or raw text. But if more information is required, a more advanced DI system will be required. Look for systems that include an extensive stamp library capable of supporting Industry 4.0.
Automation also comes into play here. More and more customers are implementing automation systems that facilitate the entire board handling and exposure process without the need for operators on every system. As more move to automating their DI systems, PCB manufacturers must have the flexibility to choose the automation vendor they prefer.
Variable wavelengths in DI systems are also necessary to allow support for a wide range of photosensitive materials. Some DI system manufacturers have adopted this capability. This flexibility enables the handling of variable wavelengths and ratios for each resist so that straighter sidewalls can be created.
High-Accuracy Registration and Address Resolution
There are two main considerations here. First, high accuracy is needed for accurately placing components on boards. If a DI system has optical or mechanical deficiencies, patterns may not be reproduced properly. Ideally, patterns are printed digitally with exact, straight lines in high resolution that perfectly match the designed pattern. The higher the address resolution, feature placement, and the better the registration, the more likely the exposed image will be an accurate representation of the intended feature.
Some DI systems can provide these levels of accuracy, and others cannot due to resolution, depth of focus, scaling capabilities, and more, so be sure to consider these factors in evaluating systems.
Lowest Cost Per Print
All manufacturers have the goal of printing boards on a DI system at the lowest cost, but this may also result in limited capabilities. Fully understanding your capability requirements should guide your decision on which system to purchase. For manufacturers producing at a wide variety of products and/or at high volume, a more sophisticated system may be more beneficial. Though the cost per print will be higher, it may better handle multiple processes—such as inner, outer, via, and solder mask—and produce more boards more quickly.
Not every manufacturer requires high throughput. But if you do, be sure to select a DI system that can meet your throughput needs while still producing high-quality boards. Some features and capabilities to consider in your evaluation should include a high-powered light source, a dual-table transport mechanism that enables one-pass imaging, smart job queues that can quickly load jobs with a barcode reader, the ability to support different panel sizes in the queue, automatic job changes, fast target acquisition time, a simple user interface, and minimal set-up time for new jobs. All of these features and functions will help to ensure that you get the highest throughput possible.
Existing Local and Service Presence
Having a local live service presence is the last but equally important consideration. It’s common sense, but sometimes it’s one that people overlook in an evaluation. As you select a DI system, determine if the system manufacturer offers on-site support with a local presence with fast response times. Since typical PCB manufacturers can’t afford to have machines down for hours or even days, knowing you have live support available at least 10–12 hours per day is very important. Also, it’s a bonus if the company has nearby customer support teams in case an on-site visit is required. Not thinking about service is a common error and one that can be a killer for quick-turn shops.