The pre-baking of flex printed circuit boards (PCB) immediately prior to assembly is an industry standard requirement that is documented in IPC2223 sec 5.3.5, IPC-FA-251 sec. 22.214.171.124.2 and by material suppliers (i.e. DuPont Pyralux Technical Manual sec. 5.23). This applies to all polyimide-based flex and rigid–flex designs. But why is pre-baking done prior to assembly, rather than earlier in the circuit board manufacturing stage?
When ordering flex circuit boards online, quick turn order delivery timelines can incur setbacks if the data set is either incomplete or if the design has technical issues. Technical issues can be related to either manufacturability or the end use of the parts. These issues then often require multiple communications to resolve and in some worst-case scenarios, extensive design revision. Any of these issues will of course delay the delivery of the finished parts.
The reason printed circuit boards (PCBs) require a surface finish rather than being left as simply bare copper is because while copper is an excellent conductor, leaving it exposed will cause it to oxidize and deteriorate over time. The increased exposure will cause the PCB to fail much sooner than expected.
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.