EMI (electromagnetic interference) and RFI (radio-frequency interference) are disturbances generated by external sources that impact a cable assembly by degrading the assembly's performance or completely preventing it from functioning. These disturbances can cause problems ranging from an increase in error rates of the signal being transmitted through the assembly to total loss of any electronically readable signal.
A printed circuit board (PCB) is an inexpensive and compact way to create many of the necessary interconnects between RF components in a subsystem. The interconnects are most often created with stripline and microstrip transmission lines, as well as vertical coaxial transmission lines created with plated through hole patterns.
A pure notch or band stop filter (also called band reject filter) works by creating a VSWR (Voltage Standing Wave Ratio) resonance over a narrow bandwidth. This creates near total reflection over that bandwidth, while having very little reflection in the surrounding pass bands. By the nature of their creation, these notch filters are typically narrow band. Bandwith comes linearly with added resonators, increasing size and loss.
When you’re in the process of designing a new product, the last thing you are thinking about is the how the product is going to be packaged for transit. However, failure to prepare for and understand electronics packaging regarding how both your components and your finished unit are going to ship is a costly oversight.
For many narrow to wide bandwidth band pass applications, pure band pass filters (also bandpass filters or BPF) are a good fit, - forming rejection bands below and above the passband in a single filter. Coupled line, combline, and interdigital are three pure band pass filter types. Pure filters can be the most efficient solutions for loss and physical footprint where the specs mandate their usage. For ultra-wideband applications, pure solutions may require too many poles making physical size too large and insertion loss too high for many systems.
I can remember the first ‘incident’ of black pad, years ago, when Epec started to use the electroless nickel immersion gold (ENIG) process. We didn’t notice the issue at the time, as it is not evident on the bare board, but received the complaint from assembly as it was later identified on completed assemblies.
If you’re a designer of RF or microwave printed circuit boards you’ve probably already selected a laminate material that is appropriate to your project, having based your choice primarily on the electrical requirements of the RF circuit, such as signal speed, loss rate etc. Be careful however not to overlook the fact that the specialty materials used in such designs also possess unusual mechanical characteristics; processing is different from that of normal FR4 boards.
Over the past several years there have been several instances where battery suppliers that manufacture the highest technology batteries have run into financial difficulties (think A123, Boston Power) or change their business model and no longer want to supply small/medium volume applications (Panasonic). This has created several problems for OEMs as they have designed these cells and have passed all of the certification testing for UL, EMI, CE and UN DOT 38.3.
What do I get for my tooling dollar? This question (in one form or another) is one that gets asked frequently. Tooling is always a concern for the customer. It’s an added cost which cannot be converted to sales and ultimately, the bottom line.