Flexible Thinking: Another PCB Design Paradigm Shift in the Works
Happy’s Tech Talk #29: Bend-to-Install Semi-flex FR-4
Connect the Dots: Five Best Practices for Designing Flex and Rigid-flex PCBs
DFM 101: Final Finishes—OSP
March 9, 2023 | Anaya Vardya, American Standard CircuitsEstimated reading time: 1 minute
Introduction
One of the biggest challenges facing PCB designers is not understanding the cost drivers in the PCB manufacturing process. The next final finishes to discuss in this series is OSP. As with all surface finishes there are pros and cons with the decision of which to use. It is a combination of application, cost, and the properties of the finish. OSP is RoHS-compliant as there is zero lead content in the finish.
Final Finishes
OSP (Organic Solderability Preservative)
OSP is a thin organic coating, typically 5.9 to 11.8 µin [0.15 to 0.30 µm] thick, designed to prevent the oxidation of copper to maintain solderability over an extended period. Compared with other surface finish technologies, OSP is somewhat different. It uses a chemical process to produce an organic film on the bare copper surface which acts as a barrier to copper oxidation. OSP is organic, not metallic, and its cost is lower than most surface treatment technologies.
As with all surface finishes, the primary purpose is to protect the solderable surfaces on the PCB from oxidation and to aid in assembly soldering. This process coats a very thin coating of an organic material that inhibits copper oxidation. It is so thin that it is nearly impossible to see and measure. The organic material is removed by the assembly flux. Boards that have been OSP coated will have bright copper pad coloration. OSP is specially designed for mixed metal applications, such as electroless nickel immersion gold (ENIG). The OSP selectively deposits on copper while leaving gold connectors or metallic heat sinks free of contamination.
There are a couple of common OSP finishes widely used in the industry:
ENTEK CU-56: This is used for assemblies that will only go through a single reflow process. This finish is not being utilized much anymore because of the use of mixed technology boards (SMT and through-hole).
ENTEK CU-106A: This is the most prevalent version primarily due to the ability to survive multiple thermal assembly operations. PCBs that have multiple surface finishes can use the CU-106A(X) finish.
To read this entire article, which appeared in the February 2023 issue of Design007 Magazine, click here.
Share on:
Suggested Items
Designers Notebook: Impact of Advanced Semiconductor Packaging on PCB Stackup
01/07/2025 | Vern Solberg -- Column: Designer's NotebookTo accommodate new generations of high I/O semiconductor packaging, printed circuit board fabrication technology has had to undergo significant changes in both the process methods and the criteria for base material selection and construction sequence (stackup). Many of the new high-function multi-core semiconductor package families require more terminals than their predecessors, requiring a significantly narrower terminal pitch. Interconnecting these very fine-pitch, high I/O semiconductors to the PCB is made possible by an intermediate element referred to as an interposer.
BOOK EXCERPT: The Printed Circuit Designer’s Guide to... High Performance Materials, Chapter 4
01/02/2025 | I-Connect007In Chapter 4, Michael Gay discusses the two main types of copper foil used for PCB boards today: electrodeposited (ED) foil and rolled annealed (RA) foil. He also explains the pros and cons of each, and provides an update of the latest innovations in copper foil technology.
Connect the Dots: Designing for Reality—Solder Mask and Legend
01/02/2025 | Matt Stevenson -- Column: Connect the DotsIn the previous episode of I-Connect007’s On the Line with… podcast, we discussed the strip, etch, and strip process. At this point, we have a functioning board, but we still need to protect the PCB from environmental effects and document the circuit components. This brings us to the solder mask and legend phase of production.
Global PCB Connections: Following DFM Rules Leads to Better Boards
12/18/2024 | Jerome Larez -- Column: Global PCB ConnectionsAs a PCB field applications engineer, ensuring smooth communication between PCB designers and fabricators is one of my frequent challenges. A critical part of that dialogue is design for manufacturing (DFM). Many designers, even experienced ones, often misunderstand or overlook important DFM considerations. They may confuse design rules with manufacturing minimums, leading to technically feasible designs that are difficult or costly to produce. In this column, I will clarify some common DFM guidelines and help designers understand the difference between “design rules” and “minimums” while sharing best practices that will simplify the production process and ensure the highest quality PCB.
Sayonara to the Last Standing Copper Foil Plant in North America
12/17/2024 | Marcy LaRont, I-Connect007In July 2021, PCB007 Magazine published an interview with Michael Coll and Chris Stevens of Nippon Denkai about the new acquisition by Nippon Denkai of the last-standing ED foil manufacturer in North America. The plant in Augusta, Georgia, was formerly owned by Oak Mitsui, Inc. and had been purchased by Nippon Denkai the previous March, after which significant investment was made with the expectation of providing more jobs.