Happy's Tech Talk #11: An Update on Inkjet Technologies

Ever since the first inkjet printer appeared from Hewlett-Packard in 1980, engineers have been trying to use it in printed circuit manufacturing. The first successful application was by HP’s PCB engineers in 1983, who created an inkjet printer mechanism to serialize each PCB with a unique S/N for traceability. They used one of the UV inks HP had developed and that worked well on circuit boards but was not suited for use on paper.

Introduction
Karl Dietz wrote on this topic when it first began to appear as a method of solder mask application and legend printing to replace screen printing. Some of his columns1 discussed the methods of inkjet printing, elements of the three types of inks (thermal, ultra-violet, and phase-change), and the print-heads used by seven current machines on the market. Today, the applications, head technologies, software and inks/pastes have been improved significantly. Inkjet is one of the technologies used in printed electronics.

Inkjet Printing

An industrial inkjet printer has four important elements, as seen in Figure 1:

  1. The printhead(s)
  2. The ink or paste
  3. The print module-ink preparation or curing
  4. System for CAM data preparation and head/substrate positioning

Happy_TT11-fig1.jpg
Figure 1: Inkjet system breakdown into four elements. (Source: Dow Electronics Materials)

Inkjet printing technology produces droplets of the ink contained in the fluid channel, with diameters ranging from 10 to 150 μm, which approximately correspond to the diameter of the nozzle (Figure 2). The volume of the droplets is in the picoliter range. Inkjet printing is suitable for electronics manufacturing due to the following reasons:

  • It is a non-contact process that selectively deposits a wide range of materials onto a wide range of substrates in a drop-by-drop manner
  • The shop floor space requirements, the initial investment, and the time to get an inkjet printing setup running are lower than most other printing technologies
  • It is suitable for a wide range of production scales, from prototyping to large-scale industrial production
  • Ink consumption and material waste are minimal
  • It is flexible regarding its positioning within a process chain
  • It can produce patterned thin films. It should be mentioned however, that manufacturing of highly complex integrated circuits (ICs) has exclusively been performed by specialized techniques deviating from standard inkjet technologies.2

Happy_TT11-fig2.jpg
Figure 2: Simplification of inkjet printing process3.

Inkjet Printheads
The printhead is the heart of the inkjet printer. In addition to the original thermal thin-film printhead of HP’s, there is also the piezo-electric head that makes up most of the additive-type of inkjet printing. Now comes the piezo-acoustic head and the continuous laser-assisted system (LIFT), as seen in Figure 3.

Happy_TT11-fig3.jpg

Figure 3: Laser induced forward transfer (LIFT) system4 and new piezo-acoustic head5.

Happy_TT11-fig4.jpgThese new technologies extend the number of inks that can use inkjet printing. The capability of a head is a function of the droplet size, its overlap, and the frequency the head can achieve, now 80 kHz. This permits resolution of 5,000 dpi and resulting minimum copper line widths of 40 to 70 microns.

To improve both speed and density, inkjetting has taken a page from the DMD micro-mirrors exposure book and now uses multiple inkjet heads to achieve this performance. Figure 4 shows a test vehicle from the Center for Microsystems Technology (CMST) of Ghent University and IMEC with etched traces down to 40 microns.

Figure 5 illustrates this etching/plating resist capability on a Samsung panel with the Samsung printhead using five pl-256 nozzles.

Happy_TT11-fig5.jpg
Figure 5: Another example of a production inner layer, before and after etching of 75/75-micron traces and spaces3.

Ink or Pastes
There were numerous challenges with ink formulation, including adhesion, curing, and especially spreading after jetting. Figure 4 illustrates the difference between general inkjet printing on paper vs. inkjet printing on a PCB.

Ink Preparation/Curing
In addition to jetting the ink, the system may have to prepare the ink (by melting a hot-melt ink) or by curing a UV ink.

System Software and Positioning
The additional system activities may include positioning of the inkjet heads and, particularly, the preparation of the CAM information to drive the inkjet heads and substrate positioning. Table 1 illustrates the printing time for a 75/75-micron traces on a 460 mm x 610 mm panel using only one head vs. 15 heads.

Happy_TT11-table.jpg

The sensitivity of print time vs. number of heads is seen in Figure 6.

Happy_TT11-fig6.jpg

For advanced systems, large panel throughput can be:

  • 17.0" x 22.8": 17 seconds
  • 20.0" x 24.0": 27 seconds
  • 24.0" x 30.7": 31 seconds

Applications
The advantages of inkjet printing as a method of solder masking and legend printing are well established. As an etch resist for inner layer etching it has an advantage down to

The market for inkjet printheads will grow to $3.3 billion by 2024 (Figure 7).

Conclusion
From its simple beginnings as a quiet way to print on plain paper, inkjetting has grown up. This is because the head technology is being modified to use a much greater variety of materials to jet. Here are 12 applications of inkjet technology, and the list is growing:

  • Antenna: For example, wireless, mobile phones, IIoT, mil/space, CB
  • Membrane switch: Keypads
  • Capacitors, resistors, and inductors
  • Shielding: For example, RFI and EMI
  • Sensors and precision interconnects
  • Photovoltaic (solar cells)
  • RFID inlays/tags and Smart cards, e-passport/ID cards
  • Electroluminescence, touch panels and other displays
  • Automotive and telecom
  • Medical and diagnostic devices
  • Heater circuits
  • Replacement of gold plating on switches

Happy_TT11-fig7.jpg
Figure 7: Prediction of the growth of inkjet printhead sales for consumer, industrial, and graphics printing. (Source: YOLE Development3)

As it competes with dry film photoresists, inkjet technology still has some significant challenges for the machine manufacturers to overcome, including making sharp corners (drops will always produce a curve), getting track edges as smooth and straight as possible, replicating standard industry practices such as tenting, and ensuring printhead maintenance programs to avoid nozzle blockages, But it’s on its way.

References

  1. Columns by Karl Dietz in The PCB Magazine: Tech Talk #73, October 2001; Tech Talk #137, February 2007.
  2. “Digital and Environmental Circuit Board Manufacturing Based on Continuous Laser Assisted Deposition,” Ralph Birnbaum, et al, IPC APEX 2022.
  3. “The Use of Inkjet Printing Technology for Fabricating Electronic Circuits—The Promise and the Practical,” by Thomas Sutter and Brian Amos, IPC APEX EXPO 2012.
  4. “Customizable Capacitive Sensor System Using Printed Electronics on Window Glass,” by Jan Frohlich, et al, SMTA Pan Pacific Symposium 2020.
  5. “Inkjet Printing for Printed Electronics,” by Ashlok Sridhar, Fraunhofer Research Institute for Electronic Nano Systems (ENAS), Material Matters, Volume 6 Article 1, 2019.

Happy Holden has worked in printed circuit technology since 1970 with Hewlett-Packard, NanYa Westwood, Merix, Foxconn, and Gentex. He is currently a contributing technical editor with I-Connect007, and the author of Automation and Advanced Procedures in PCB Fabrication, and 24 Essential Skills for Engineers.

This column originally appeared in the August 2022 issue of PCB007 Magazine.

 

Back

2022

Happy's Tech Talk #11: An Update on Inkjet Technologies

08-30-2022

Since the first inkjet printer appeared from Hewlett-Packard in 1980, engineers have been trying to use it in printed circuit manufacturing. The first successful application was by HP PCB engineers in 1983 that created an inkjet printer mechanism to serialize each PCB with a unique S/N for traceability. They used one of the UV inks HP developed that worked well on circuit boards but not suited for use on paper.

View Story

Happy’s Tech Talk #10: Optical Alignment/Coupon Welding for Stackups

08-02-2022

In this month’s column, I will discuss optical alignment for pinless lamination stackup, a topic that complements the induction lamination in my November 2021 column. Pin tooling plates have been used for lamination since it first started sometime in the 1960s. I first encountered multilayer stackup when I was assigned to increase capacity for our multilayer output in 1972. This was to accommodate the growth of our computer business. Unfortunately, the explosive growth of our calculator orders in 1973 required that we look for numerous vendors to produce the six-layer logic board in the HP-35 calculator.

View Story

Happy’s Tech Talk #9: Radars, Missiles, and the World’s Costliest Computer

07-19-2022

Let’s have a little fun and walk back nearly 70 years into the history of electronics and computers. What was the world’s costliest computer and why? The answer is not today’s supercomputers, nor computers built during World War II. Instead, it lies in a real-time air defense radar system built during the height of the Cold War of the 1950s that had left the U.S. extremely vulnerable to a Soviet bomber attack. This was the beginning of a North American strategic defense system, eventually known as the Semi-Automatic Ground Environment System (SAGE).

View Story

Happy's Tech Talk #8: Copper Etchant Regeneration

05-31-2022

Copper has become a valuable metal, and with the growth of EV has come higher currents needed in PCB with increasing weight of copper in PCBs. This creates the need for increased copper etching and consumption of copper etchants. Today, in an effort to recoup some of that cost, increasingly more extraction and recovery units are being installed in PCB facilities around the world. Annual profit generation from recovering copper and regenerating PCB etchants has the potential to reach six figures.

View Story

Happy's Tech Talk #7: Next Generation Application Specific Modules

05-02-2022

In 1965, Gordon Moore predicted that the number of transistors that could be packaged into a square inch of space would double every year for the near future. Although his projection was later revised to every 18 months, Moore’s Law has withstood the test of time for five decades. Today, we are beginning to see obstacles to this type of exponential growth due to the inherent limits associated with silicon lithography, packaging of the devices, and component placement on PCBs.

View Story

Happy's Tech Talk #6: Looking at the Process of Repanelization

03-28-2022

I have spent many years in printed circuit fabrication, including nearly 20% of my career in Asia. One problem that concerns all fabricators is the issue of “How many ‘X-outs’ are allowed per assembly sub-panel array? Here are a couple of solutions I have used and encountered in my travels.

View Story

Happy's Tech Talk #5: Advanced Boards for Heterogeneous Integration

03-07-2022

The expansion of IC functionality usually progresses with the shrinking of IC geometries, called “Moore's Law” after Gordon Moore who first coined the phrase. But now that geometries are below 5 nm, the costs and difficulties are creating a barrier to much further advances. So, the solution seems to be to mix IC die on the same substrate as a system-in-package (SiP) that is now called heterogeneous integration (HI).

View Story

Happy's Tech Talk #4: Semi-Additive Processes and Heterogeneous Integration

01-31-2022

The semi-additive processes (SAP) are not new. I first used them with a novel process back in 1978. MacDermid had a novel SAP process called PLADD II (PLAted Additive). It was an anodized aluminum foil applied to laminates that we could easily etch off after drilling and continue with a special electroless copper for thin metallization.

View Story
Back

2021

Happy's Tech Talk #3: Photonic Soldering

12-20-2021

Printed Electronics (PE) continues to be a growing technology. But one of the advantages, as well as a drawback is using low-cost substrates, like paper, that cannot take the temperature of solder paste reflow. Also, the inks need to be cured. One current way to cure the printed inks is with ultraviolet radiation curing, such as used with solder mask or legend inks.

View Story

Happy's Tech Talk #2: Induction Lamination

11-23-2021

Multilayers have been around about as long as the printed circuit. The industry has always used heated hydraulic lamination presses to produce these multilayers, with the introduction of vacuum assist in the 1980s. But recently, with the encouragement of GreenSource Fabrication, induction lamination has been perfected by Chemplate Materials of Spain. Chemplate had introduced the use of induction-pinning by optical alignment of innerlayers for multilayer stackup in the early 2000s. This was to go with another innovative way to laminate innerlayers together—the Italian CEDAL resistance-foil vacuum-press, which had some early adopters.

View Story

Happy’s Tech Talk #1: Vertical Conductive Structures (VeCS)

10-22-2021

The industry has not had many new structures in the last 60 years. Multilayers have continued to evolve with thinner materials, smaller traces / spaces as well as drilled vias. It’s been nearly 40 years since Hewlett-Packard put their first laser-drilled microvia boards into production for their innovative Finstrate process.

View Story
Back

2017

Happy’s Essential Skills: Tip of the Month—The NIST/SEMATECH e-Handbook of Statistical Methods

07-05-2017

In the 1990s, the National Bureau of Standards was distributing a popular statistical document, the Handbook 91, written by Mary Natrella of the NBS Statistical Engineering Laboratory. A request by Patrick Spagon of the Statistical Methods Group of SEMATECH to update the NBS Handbook 91, Experimental Statistics, led to the creation of a project team from NIST and SEMATECH to create a new web-based statistical handbook including statistical software.

View Story
Back

2016

Happy's Essential Skills: Understanding Predictive Engineering

12-16-2016

New product realization and design for manufacturing and assembly (DFM/A) have now started to become more visible as programs that can improve a company’s time-to-market and lower product costs. Many programs are underway by many companies and what is now needed is a framework to coordinate the application of these programs. This column will cover the interactions of DFM/A and the need for development of a new framework to coordinate the trade-offs.

View Story

Happy’s Essential Skills: Technology Awareness and Change

11-22-2016

From Happy Holden: A long-time printed circuit-industry friend of mine, Martin Tarr, an instructor at University of Bolton, UK, is a leading expert on change. He wrote an excellent tutorial for his university course on electronics manufacturing. With permission from Tarr, I am including a portion of it here as the basis of this column, starting after the graph in Figure 2. But first, a few thoughts of my own.

View Story

Happy's Essential Skills: 10-Step Business Plan Process

11-03-2016

It takes more than just a good idea to exploit that brainstorm of yours. Hewlett Packard’s “10-Step Business Plan Process” is the format to present an idea or product in a fashion that will answer most questions that management may have about a product or idea.

View Story

Happy's Essential Skills: Lean Manufacturing

10-19-2016

Lean doesn’t have to exist in manufacturing alone. Lean is a fairly recent principle that can apply to all of our goods and services. For those of you not familiar with Lean, I recommend the free E-book "Survival Is Not Mandatory: 10 Things Every CEO Should Know about Lean" by Steve Williams, a regular columnist for I-Connect007.

View Story

Happy's Essential Skills: Metrics and Dimensional Analysis

10-05-2016

After 20 of my columns, readers probably realize that I am an analytical person. Thus, I dedicate this column to metrics—the method of measuring something. I mentioned the four levels of metrics in my June column "Producibility and Other Figures of Merit." I also introduced the five stages of metrics in the second part of the column "Design for Manufacturing and Assembly, Part 2." This column completes the discussion with a look at dimensionless quantities.

View Story

Happy’s Essential Skills: Recruiting and Interviewing

09-29-2016

Hopefully, your career has progressed to the point that you are empowered to recruit your own team or a key person for your team. There are always technical people looking for better jobs, but many times, the most talented are busy doing their work and not looking for a new opportunity.

View Story

Happy’s Essential Skills: Computer-Aided Manufacturing, Part 2 - Automation Examples

09-22-2016

Semiconductor fabs like to avoid writing custom software to fit all of the idiosyncrasies of individual processing systems. So HP developed PC-10 to handle IC process equipment by separating it into general classes. SECS II was a mandatory prerequisite of the equipment before an interface to PC-10 could be developed.

View Story

Producibility and Other Figures of Merit

06-10-2016

Metrics are data and statistically backed measures. It is always expedient to base decisions on data and metrics, for example, in PCB design. These measures can be density, first-pass yield connectivity or in this context, producibility. These measures are the basis for predicting and planning a printed circuit design. But what if a metric doesn’t exist? Then you can create the next best measure, the Figure of Merit

View Story

Learning Theory/Learning Curves

06-01-2016

Learning is not instantaneous! Nor is progress made in a steady manner, but at a rate that is typified by one of two basic patterns. In some cases, plateaus will be seen in learning curves. These are caused by factors such as fatigue, poor motivation, loss of interest, or needing time to absorb all the material before progressing to new. This column will not go into details of how learning is achieved, but will summarize some of these theories.

View Story

Happy’s Essential Skills: Project/Product Life Cycle

05-18-2016

The product, and or project (process) life cycle (PLC) is fundamental to a corporation intent on developing new products or processes. It sometimes is called the new product introduction (NPI) process but that is only half of the life cycle. There is product support, enhancement and eventually, obsolescence.

View Story
Copyright © 2022 I-Connect007. All rights reserved.