Controlled impedance needs. The HDMI video input had a number of various needs for controlled impedance. The size of the trace used was extremely little, and the signals were reasonably slow-moving compared with DDR, so trace size had not been an issue. Nonetheless, the HDMI needed 100Ω differential pairs, while the memory ran at 80Ω. Consequently, it was a fascinating obstacle to ensure controlled impedance, and it was hard ahead up with a rigid flex PCB stackup that would leave appropriate area for 80Ω, as well as 100Ω, without ending up being also slim and hard for PCB manufacturers to make.
HDI PCB and blind and hidden vias PCB were related to break out traces from the HDMI and FPGA controller. The HDMI controller pattern additionally utilized via-in-pads. It served to do some “what-if” scenarios and see exactly how the HDI stackup might potentially come out. We went through a couple of versions on that with a couple of various kinds of materials, considering the impedance control preparation.
At first, FR-4 material was under consideration, but after some screening, we decided to opt for a material that had a lower dielectric constant, attaining reduced loss, signal stability and preferable line-space ratio for impedance controlled traces.
Utilizing HDI PCB lowered the number of layers required in the board generally, and after stabilizing the cost with the benefits of HDI PCB innovation, it was chosen this was the appropriate instructions.
There were 3 rigid sections in the final design:.
1) A main section with the FPGA, DDR3 ICs, and power supply devices;.
2) an area with slower, analog-type components and more power materials;.
3) an area that featured an extremely tiny HDMI receiver with numerous feasible positionings to suit the inbound input cable.
The rigid flex PCB option. As the design moved forward and it became clear that office was an issue, it was chosen to link the rigid boards with a flexible bow to avoid utilizing typical physical adapters that called for even more area.
The final rigid flex PCB stackup was 10 layers. The rigid boards used eight layers and lugged all the impedance-controlled and high-speed traces. The other 2 layers were the flex PCB signal layer, which was also used as the VCC layer generally rigid part of the board. There was some cooperation in between layers of the rigid and flex sections, however, for one of the most part these were dealt with individually.
Rigid Flex PCB allowed the board to fit into the small housing on the helmet-mounted screen system. The flex bow could bend a variety of ways, accommodate various angles, and be rolled up and fully consumed within the quantity of the container, providing options on exactly how the boards would certainly participate in the system and twist around the optical parts.
Anything that needed impedance control was handled completely within among the rigid structures. Simplifying into those sections permitted us to stay clear of any type of need for impedance control on the flex, which was a big win insofar as price goes.