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For North America, there is a growing need for more ultra-high density HDI capability. Some of the reasons for the slower adoption of SAP/HDI fabrication may rest with two obstacles: Subtractive processes have difficulty as they approach 50-micron traces and spaces (0.002”), and it is not clear what the total system acquisition costs will be for ultra-HDI.
As PCB geometry begins to require 50-micron traces/spaces, subtractive processes start to have yield and imaging problems. Semi-additive processes (SAP) are the chemical processes that are used for these applications. My column in the January issue of PCB007 Magazine outlines the various SAP processes used by our industry. The other factor is the uncertainty in how much is ultra-HDI is going to cost. This forms a real obstacle for implementation of SAP. One reason may be the absence of density metrics. Performance measures are needed for the difficulty to assemble surface-mounted components with fine-pitch; the amount of density required on the printed circuit to mount all these fine-pitch devices in the area provided.
In my opinion, the primary goal for PCB development process engineers to implement new customers’ new products and/or new processes as part of expanding the business. As Figure 1 shows, implementing new technology is an “S-shaped curve.” Lastly, it supports a strategic plan that the owners or the CEO have in terms of what is the long-term goal that you can constantly be working on. Risk reduction is one of those tasks.
Although the rewards for ultra-HDI or an SAP process are very concrete, the PCB designer may be more focused on the risks. In the development process, the risks to the customer need to be articulated and adequate solutions developed that allow the rewards (higher density) to tip the scales in favor of its adoption.
This was true for me in popularizing HDI in the late 1980s. Hewlett-Packard had developed laser drilling because of a need for low-inductance blind vias on its Finstrate COB in 1982. Publications about the technology in the HP Journal and at the IPC Technology Forum interested some OEMs like Siemens and IBM, but many OEMs had a “wait and see” attitude. It was not until HP proposed an alternative design to a new device called the “cellular phone” in 1993, that Japan jumped on HDI for mobile phone boards.
To read this entire article, which appeared in the February 2022 issue of PCB007 Magazine, click here.