Characteristics of a third-level PCB assembly: or why parts should be 'implemented,' not just 'installed.'.

Author:Khan, Mueed

By and large, PCB assembly up to now has been rather traditional. Surface mount technology has made significant inroads to account for the greater majority of assembly technology compared to through-hole.

However, these days PCB assembly takes on new levels of technology, complexity and service requirements differently. At level one, OEMs require standard assemblies based on standard, defined processes and expect 100% yields, or close to them.

At level two, challenges are involved, but the technology and OEM expectations are defined, and yields are relatively high. Generally, the OEM customer conveys their expectations in terms of the latest IPC revision, functionality and performance. With that information, the EMS provider moves on to develop the process and fulfill the OEM's requirements.

A new "level three" is beginning to be recognized on the assembly floor. In this case, the OEM customer's expectations aren't very defined, even to themselves. Under typical circumstances, a design is not known to be successful until a working prototype is built. For the contract manufacturer, it is imperative to understand those OEM expectations, and to determine ways to handle the project and use a package "implementation" approach, rather than package "installation" approach, to comply with those requirements.

What defines this third level of assembly? PCB assemblies that can best be characterized as changing and evolving and becoming extensively complex in terms of packages used; high frequency (above 5GHz); the assembly requirements, and of course, customer expectations. For instance, a third-level assembly would be a digital board with a high-density, extremely populated landscape, or a highly integrated, double-sided, fully populated board with pBGAs, DSPs, LGAs, digital wafer-level packages, and miniatures such as 01005 passives.

This third level harbors a considerable number of gray areas, such as the process option for high-density digital population, which could be very different than that needed for a microwave/RF assembly. The tooling and processes for a successful prototype build will vary accordingly.

High-frequency digital, microwave and RF assemblies closely match this third level of assembly insofar as the similarity of challenges (FIGURE 1). The commonality is that the EMS provider and OEM must develop a comprehensive approach to fabrication and design for manufacturing (DfM), design for assembly (DfA), and design for test (DfT) for...

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