-
- News
- Books
Featured Books
- pcb007 Magazine
Latest Issues
Current IssueAdvancing the Advanced Materials Discussion
Moore’s Law is no more, and the advanced material solutions to grapple with this reality are surprising, stunning, and perhaps a bit daunting. Buckle up for a dive into advanced materials and a glimpse into the next chapters of electronics manufacturing.
Inventing the Future With SEL
Two years after launching its state-of-the-art PCB facility, SEL shares lessons in vision, execution, and innovation, plus insights from industry icons and technology leaders shaping the future of PCB fabrication.
Sales: From Pitch to PO
From the first cold call to finally receiving that first purchase order, the July PCB007 Magazine breaks down some critical parts of the sales stack. To up your sales game, read on!
- Articles
- Columns
- Links
- Media kit
||| MENU - pcb007 Magazine
Being Flexible in a Rigid World
May 21, 2015 | Michael Carano, RPB Chemical TechnologyEstimated reading time: 3 minutes

With double-digit growth in the foreseeable future, flexible printed circuits (FPC), have found a tremendous niche as an enabler for various electronic applications. This trend is expected to drive the need to increase productivity while improving performance and reducing costs. Of course, in order to sell FPC, one must tackle the unenviable task of metalizing these often difficult-to-plate materials. In particular, the deposition of metal on a polyimide film is discussed. When discussing adhesion of a deposited metal to a substrate, one must focus on two distinct but related processes. The first relates to surface preparation conditioning and the second to the deposition of the metal itself.
Preparing the Polyimide Surface
One common theme that electroplaters often here is surface preparation. Materials such as polyimide are prone to low copper adhesion. To mitigate this situation, specially formulated conditioners are employed to provide a surface that is conducive to adhesion. Any surface that one desires to deposit another coating on requires that surface to be activated. Otherwise, defects (Figure 1) are often found. Generally these defects include:
- Blistering
- Peeling
- Voids
One critical step in the process sequence is to utilize a conditioning agent (prior to electroless copper metallization) that makes the polyimide material more susceptible to adhesion of the palladium catalyst. In turn, the conditioning agent enhances the adhesion of the subsequently plated copper to the polyimide.
As is often the case, electroless copper plating process systems include a second conditioning step after polyimide etch. While this author recommends such a step, it is with reservation. Basically, the second conditioning step must contain materials that are free rinsing so as to not leave a film on the polyimide. Such a film may lead to a barrier that reduces adhesion of the copper deposit. Should such a situation arise, the fabricator would be better served to run a performance test with no extra conditioner, one with 50% of the recommended concentration, and one test with the full recommendation. Then after plating, perform a tape test to quantify the adhesion, or lack thereof.
Electroless Copper Deposition
The importance of the conditioning step not withstanding, total success is not achievable without a low stress electroless copper deposit. Typically, deposited metals exhibiting a high degree of internal stress find it necessary to “pullaway” from the substrate in order to relieve the stress condition.
The literature reviews and basic research studies provide evidence that the grain structure of the copper deposit influences the deposit’s adhesion to the copper interconnect.
Microsections taken from test boards processed in different electroless copper process formulations show vastly varying structures. As shown in Figure 2, the structure is one that is considered a finely grained crystal structure that appeared “loose.” From multiple testing programs, this type of structure was more prone to hole wall pullaway and over all poor adhesion.
In Figure 3, the structure shown has a high correlation to good interconnect reliability, as determined by IST and thermal shock testing. In addition, this type of deposit structure exhibited very low stress and provides excellent adhesion when subjected to tape testing. It is highly recommended that for flex circuit applications, especially dynamic flex, maximum adhesion of the copper to the substrate be achieved. Further, the data supports the assertion that a low- to medium-deposition electroless copper process be employed for flexible circuit manufacturing. These types of electroless copper processes typically provide a low stress deposit with a fairly large grain structure.
This is not to say that direct metallization processes are not compatible to flex circuit fabrication. On the contrary, direct metalization is very proficient with respect to flex and will be reviewed in a future post.
About the Author:
Michael Carano is with RPB Chemical Technology. He has been involved in the PWB, general metal finishing photovoltaic industries for nearly 30 years and is currently co-chair of the IPC Technology Roadmap Executive Committee. Carano holds nine U.S. patents in topics including plating, metallization processes and PWB fabrication techniques. He was inducted into the IPC Hall of Fame in 2014 and has been a regular contributor to various industry publications throughout his career.
Testimonial
"Our marketing partnership with I-Connect007 is already delivering. Just a day after our press release went live, we received a direct inquiry about our updated products!"
Rachael Temple - AlltematedSuggested Items
Trouble in Your Tank: Implementing Direct Metallization in Advanced Substrate Packaging
09/15/2025 | Michael Carano -- Column: Trouble in Your TankDirect metallization systems based on conductive graphite are gaining popularity throughout the world. The environmental and productivity gains achievable with this process are outstanding. Direct metallization reduces the costs of compliance, waste treatment, and legal issues related to chemical exposure. A graphite-based direct plate system has been devised to address these needs.
Closing the Loop on PCB Etching Waste
09/09/2025 | Shawn Stone, IECAs the PCB industry continues its push toward greener, more cost-efficient operations, Sigma Engineering’s Mecer System offers a comprehensive solution to two of the industry’s most persistent pain points: etchant consumption and rinse water waste. Designed as a modular, fully automated platform, the Mecer System regenerates spent copper etchants—both alkaline and acidic—and simultaneously recycles rinse water, transforming a traditionally linear chemical process into a closed-loop system.
Driving Innovation: Depth Routing Processes—Achieving Unparalleled Precision in Complex PCBs
09/08/2025 | Kurt Palmer -- Column: Driving InnovationIn PCB manufacturing, the demand for increasingly complex and miniaturized designs continually pushes the boundaries of traditional fabrication methods, including depth routing. Success in these applications demands not only on robust machinery but also sophisticated control functions. PCB manufacturers rely on advanced machine features and process methodologies to meet their precise depth routing goals. Here, I’ll explore some crucial functions that empower manufacturers to master complex depth routing challenges.
Trouble in Your Tank: Minimizing Small-via Defects for High-reliability PCBs
08/27/2025 | Michael Carano -- Column: Trouble in Your TankTo quote the comedian Stephen Wright, “If at first you don’t succeed, then skydiving is not for you.” That can be the battle cry when you find that only small-diameter vias are exhibiting voids. Why are small holes more prone to voids than larger vias when processed through electroless copper? There are several reasons.
The Government Circuit: Navigating New Trade Headwinds and New Partnerships
08/25/2025 | Chris Mitchell -- Column: The Government CircuitAs global trade winds continue to howl, the electronics manufacturing industry finds itself at a critical juncture. After months of warnings, the U.S. Government has implemented a broad array of tariff increases, with fresh duties hitting copper-based products, semiconductors, and imports from many nations. On the positive side, tentative trade agreements with Europe, China, Japan, and other nations are providing at least some clarity and counterbalance.