What Is mSAP?
Modified Semi-Additive Processing (mSAP) is a fabrication approach designed to overcome the limitations of traditional etching in Printed Circuit Board (PCB) industry.
Rather than beginning with a thick copper layer and removing most of it, mSAP starts with a thin copper seed layer. Copper is then selectively plated only where circuitry is required. The result is dramatically improved line definition, finer trace geometries, and higher routing density compared with conventional subtractive methods.
The figure below gives a perspective of the differences in manufacturing capabilities on a scale:
It is important to recognize that from a manufacturing perspective at AmTECH Microelectronics, for wire bonding and other processes, traditional PCB fabrication has looser tolerances than mSAP and SAP, which have a proclivity to be more precise. As a result, during design for manufacturing it is important to talk openly with PCB fabricators that engage in traditional subtractive processes the risk of over etching to mitigate risk when fabricating boards to meet your specifications.
A Brief History: From Routing Boards to Performance Platforms
Traditional PCB manufacturing evolved during an era when boards primarily served as platforms for connecting components. The dominant process, known as subtractive fabrication, starts with a sheet of copper and removes unwanted material through photolithography and chemical etching.
For decades, this approach was more than sufficient. It was during this same era, in 1993, that AmTECH was founded in Silicon Valley, building its early reputation on precision assembly and packaging for the microelectronics industry as demand for more complex, miniaturized devices began to take shape. However, the rapid growth of smartphones, wearables, AI accelerators, and 5G infrastructure created demand for higher routing density, smaller footprints, and better signal performance. IPC's HDI design standards helped define the industry's move toward High-Density Interconnect (HDI) technologies, which introduced microvias, finer traces, and more sophisticated layer structures to support miniaturization.
The Challenge Facing Conventional PCB Fabrication
Traditional subtractive fabrication remains the most widely used PCB manufacturing method because it is mature, reliable, and cost-effective.
The challenge arises as trace dimensions continue to shrink.
In advanced HDI designs, routing density requirements often exceed what conventional etching processes can efficiently produce. As trace widths decrease, undercutting during the etching process makes it increasingly difficult to maintain geometrical accuracy, yield, and signal integrity. IEEE publications on HDI manufacturing consistently identify fine-line fabrication and miniaturization as major technical challenges for next-generation electronic systems.
The industry's response has been the adoption of additive and semi-additive manufacturing technologies.
A problem the industry faces is the shortage of qualified ITAR suppliers within the United States that support mSAP & SAP capabilities. This key industry gap in the supply chain is especially important to highlight at a time when global politics are reaching an inflection point and deglobalization and national security risks are real issues.