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Six-Layer PCB Funnel Design

Circuitry inside a mass spectrometer

Mass spectrometer circuitry

Most--if not all--electrical engineers know about Nikola Tesla’s work. A thin sliver of that number may also know that Tesla claimed to invent a charged particle beam projector --or in science fiction terms--an ion cannon. Tesla designed the Teleforce as a defensive deterrent that could create a wall of power around a country.

Although never built, Tesla’s Teleforce structure would have inspired awe. Imagine a tall shaft supporting a round somewhat bulbous top. Tesla’s plans show that the shaft would surround an ionized stream of air while the bulbous top held a charge around the tower. If an enemy aircraft appeared 200 miles away, a cannon-like beam gun would emerge from the top and shoot down the airplane with a repelling force.

Sound cool? Well, yes, but maybe not as cool as a PCB design funnel.

It’s Not a Cake

Although a six-layer PCB design funnel could conjure up mental images of a tasty funnel cake, the resemblance ends there.

When first developed during the 1990s, the point soldered stacks of metal electrodes made up the funnel.  Standard six-layer PCBs with integrated planar electrodes also served as the signal distribution network. Planar electrodes consist of an unshielded electrode embedded in an insulated plane.  The design of a planar electrode maintains an electrode surface flush with the surrounding plane.  

Newer PCB technologies have allowed modern six-layer PCB funnel designs to transition from the standard PCB design to a flexible circuit board rolled into a funnel shape. Using flexible PCBs reduces manufacturing costs.

Planar Funnels and Pushing to Multilayer Circuit Designs

For planar funnel applications, the rolled flexible PCB serves as a signal distribution circuit and as a 3D printed scaffold that forms the funnel shape. As a result, the copper planar electrodes etched into a flexible PCB function as the ring electrodes for the funnel. The funnel design of the scaffold places the electrodes in a decreasing inner diameter sequence that focuses the ion cloud for transport. In addition, the arrangement of the funnel functions as a 1nF capacitor that serves as the capacitive load for a resonant LC circuit.

The capacitive load allows the funnel to withstand high electric fields superimposed with RF voltages. In earlier circuits, the frequency of the resonant LC circuit changed because of changes in the tank coil inductance. In turn, varying the frequency manipulated the size of the m/z transmission window. The use of digital technologies improves the precision of this technique by using a supplied logic input signal taken from a Field Programmable Gate Array (FPGA) to cause the change in frequency.

Six Layer PCB Funnel Design and Flex PCB Applications

Flexible PCB technologies support the high-density electronic circuits used for multilayer funnel applications through thinner layers, finer lines, and unique shapes. While manufacturers continue to produce three-layer flex circuits that include an adhesive layer, the need for advanced applications has led to the development of two-layer flex circuits. Rather than depositing the copper into a bonding adhesive, a two-layer flex circuit deposits copper onto the polyimide to provide an extremely thin PCB that has very fine line spacing.

The production of thinner flex PCBs requires Design for Manufacturing tools that provide automatic joint curving and surface smoothing as well as automated coverlay and solder mask optimization. Electronic Design Automation (EDA) software that supports flex design gives engineers the ability to review designs before, during, and after each process and the ability to check constraints.

The manufacturing process for very thin, multilayer, flexible circuit boards utilizes laser-driven technologies. Ultra-violet laser drilling technologies can accurately drill small diameter vias through copper and polyimide layers. Precise laser manufacturing processes also provide accurate routing. Laser Direct Imaging (LDI) increases the accuracy and precision needed for producing uniform fine lines and the ability to compensate for any distortions in the polyimide flex material that occur during production.

A flexible printed circuit

Flexible circuit design

Exemplary Funnel Design Applications

Mass spectrometry is an invaluable tool for scientists, but did you know its function is dependent on advanced PCB technology? Let’s talk a bit about this technology and the role of PCB funnel design. 

An atom or molecule that loses or gains one or more electrons has a net electrical charge and is an ion. In turn, a magnetic field can deflect the path of an ion. The amount of deflection depends on the mass of the ion and the number of positive charges on the ion. An ion that has a greater number of positive charges will deflect more than an ion with fewer positive charges.

Researchers can use mass spectrometry to analyze ions associated with protein complexes and viruses that coexist in the same regime--or space. The analysis achieved through mass spectrometry measures the mass-to-charge ratio (m/z) of positive ions. Achieving this measurement allows scientists to identify unknown compounds, measure the mass in megadaltons (MDa) of individual compounds or components, and to learn more about the structure and chemical properties of molecules.

Within a mass spectrometer, an ionization source converts molecules to gas-phase ions as the first step leading to analysis. Accelerating the ions brings each ion to the same kinetic energy. Deflecting the ions effectively sorts the ions according to mass.

The “mass” portion of mass spectrometer refers to the use of a mass analyzer to sort ions according to the mass-to-charge ratio. Ion detection detects the beams of the ions passing through the spectrometer. Coupling ion detection with a data system completes the measurement through the analysis of the mass-to-charge ratio. Plotting ions found in a sample against their intensity produces a mass spectrum and a graphical representation that compares different molecular weights obtained through the m/z ratios. Every peak in the mass spectrum indicates the presence of a unique component in a m/z ratio.

Radio-frequency ion funnels can increase the efficiency of ion transmission for the transfer ions into a mass spectrometer. An RF funnel extracts ions from air into a vacuum. The ions produced in the spectrometer ionization chamber require a free path through the machine. Operating in a vacuum eliminates any air molecules that can impede the free path of the ions. Transferring ions occurs through a process called ambient ionization--or the transfer of ions from an ambient pressure to the high vacuum environment. Along with transferring ions, ambient ionization allows scientists to sample ions from a solution.

Whether building advanced flexible PCB designs or simpler circuits, Cadence Allegro gives you access to the best PCB design and analysis tools available. Once you’ve created a PCB layout, Cadence has a suite of SI/PI Analysis Point Tools for post-layout verification and simulation.

If you’re looking to learn more about how Cadence has the solution for you, talk to us and our team of experts.