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Best To Get A Fix On Third Level PCB Assembly

A majority of OEMs may be lulled into thinking that PCB assembly remains relatively static with little to no change. However, a new level three is beginning to be recognized on the assembly floor. In this case, OEM customer expectations aren’t clearly defined either to the EMS Provider or even to themselves.

At level one, OEMs require standard assemblies based on standard defined processes, and they expect 100 percent yields or pretty close to it. At level two, challenges are involved. However, the technology and OEM customer expectations are defined, and yields are relatively high. Generally, the OEM customer conveys his expectations in terms of the IPC latest revision, functionality, and performance. With that information, the contract manufacturer (CM) or EMS Provider moves on to develop the process and fulfill the OEM’s requirements.

In normal cases unless you run a first successful prototype, you cannot say if the design is successful or not. But, for the CM or EMS Provider, it is of utmost importance to understand those OEM anticipated 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.

With the rapid advances experienced in PCB assembly, it’s a good idea to get a better understanding of this third level for a successfully completed project. For greater details, check out our article on this topic.

In the meantime, here are some tips for getting a better handle on third level PCB assembly.

  • It’s characterized as constantly evolving and extensively complex as far as packaging, high frequency, assembly requirements, and customer expectations.
  • A considerable number of new challenging gray areas are involved demanding greater brainpower and smarter experimentation.
  • Design verifications, performance optimizations, noise, and EMI issues play critical roles and demand greater attention.
  • Especially with high-speed assemblies, it’s critical to confirm that the PCB is in compliance with OEM requirements.
  • Implementing rather than installing packaging is of paramount importance at level three assemblies.
  • That implementation process takes into account LGAs, micro BGAs, high-count BGAs, die-scale packages, package-on-package (PoP) and RF filters to avoid losing performance, minimizing noise, and correctly handling heat transfer issues.

Fig. 1 -- Head-on-PillowAt third level PCB assembly, packaging requires a considerable amount of extra expertise and attention. In particular, high-count BGAs have certain gray areas. For example, to deal with and compensate against head-on-pillow defects (Fig. 1), a new approach is to include a little extra copper on the outer pads.

Also, for micro BGAs and CSP packages during assembly and when performing thermal profiling, it’s important to place at least three to four thermocouples covering all BGAs to make sure that temperature variation is not more than five degrees Celsius. Also, time above liquids (TAL) should be even throughout the BGA package, and the assembly should not go through any warpage when it is going into the re-flow and cooling cycle. Otherwise, the proper re-flow fixture is required in some cases to avoid those head-on-pillow and other assembly defects.