Custom-Printed Circuit Board Development by LLE's Electronics and Controls Engineering Group

October 2015

Automated "Pick and Place" machine applies surface mount components to an LLE-designed circuit board

The 24 engineers and technicians who form the Electronics and Controls Engineering Group at the University of Rochester's Laboratory for Laser Energetics (LLE) have procured new equipment to efficiently construct custom-printed circuit boards (PCB's). Custom PCB prototypes, which are applied to laser-fusion research, can be designed, assembled, documented, tested, and corrected in-house in just a matter of days.

A PCB, most often found in a variety of electronic devices, is a thin board made of fiberglass, composite epoxy, or other laminate material. Conductive copper pathways are etched or "printed" onto the board, connecting different components on the PCB, such as transistors, resistors, and integrated circuits. From LLE's perspective, in-house circuit board prototyping has eliminated waiting for external suppliers. It has also enabled LLE to respond nimbly and with specificity on-site: "Our needs are unique (in custom function and low quantity) and it is more economical and timely to do it ourselves on-site," explains David Lonobile, Electronics and Controls Engineering Group Leader.

Engineering circuit design, analysis, and optimization activities performed at LLE's Electronic Design and Fabrication Facility are supported with digital, analog, and radio-frequency (rf) software utilities. The facility features a full complement of rf, microwave, and high-bandwidth analytical measurement instrumentation. Three-dimensional electromagnetic modeling, using commercial software, facilitates electromagnetic-pulse analysis. High-bandwidth probes coupled to high-bandwidth oscilloscopes enable electric- and magnetic-field measurements.

Engineering personnel design hardware and software using embedded microprocessors for control, instrumentation, and data-acquisition applications. Custom electronics systems are frequently developed for laser-fusion applications. Examples include:

  • a highly distributed control system on OMEGA based on Neuron microprocessors,1 which facilitates the remote control of approximately 400 mirrors, 350 rotating wave plates and linear stages, and 500 flip-in devices from the beamline operator's console;
  • negative-feedback stabilization systems, based on acousto-optic and electro-optic devices for OMEGA master oscillators and regenerative amplifiers;
  • precision-geometry stripline circuits and biasing networks needed to shape front-end OMEGA optical pulses;
  • multikilovolt, nanosecond-rise-time, Pockels-cell pulsers for optical isolation and switch-out systems;
  • precision timing circuits that synchronize instrumentation remotely located throughout the Omega Laser Facility to within 25 ps of the laser seed pulse;
  • electronics for the remote computer control of high-speed streak-camera instruments for electron-beam focusing, positioning, and sweeping functions;
  • machine controls and instrumentation for cryogenic target filling and handling, including robotic manipulators, pressure controls for target permeation, and temperature controls for ice layering.

Research Engineer Wade Bittle shown inspecting an all-solid-state Pockels-cell driver developed by LLE and including many custom-printed circuit boards

Evaluation-breadboard, prototype, and full production-grade electronics circuit boards can be developed from schematic design to full assembly through the use of in-house tools. The physical layout of single and multilayer circuits from a circuit schematic design uses Altium software. Single-layer prototype boards may be manufactured on site using a ±25-µm precision CNC end-mill router (T-Tech2 Model QC-7000-HS) programmed directly from the Gerber file output generated from Altium. Final quality PCB's require plated through-holes, solder mask, and silk screening. These are ordered from outside vendors via e-mailed files and may arrive from local Rochester businesses or from as far away as California within days.

Surface-mount components can be installed on circuit boards with a fine-pitch stencil printer that applies the solder paste, component placement with a manual or automatic pick-and-place machine, and oven reflow soldering to complete the assembly. Optical inspection and repair of circuit boards use a combination of a video microscope inspection system and a hot-air/infrared rework station.

The Electronics and Controls Engineering Group regularly plays a role in undergraduate, graduate, and high school student education. Typically, an average of two undergraduate electrical engineering co-op students from local colleges work as full-time assistants to supplement the LLE labor force. Each year many students learn basic wiring, soldering, circuit board fabrication, assembly, and electronics testing skills while experiencing full-time employment during work blocks of three months' duration. Returning students often assume greater engineering responsibilities to supplement this hands-on experience. Engineering, physics, and optics graduate students receive guidance in electronics design, fabrication, and troubleshooting relevant to circuits and equipment used in their thesis research.

The exacting research, skill, and drive to produce the broad range of custom-printed circuit boards at LLE are symptomatic of the agility and aptitude that move LLE ever closer to understanding what makes ignition happen.

1Echelon Corporation, San Jose, CA 95126
2T-Tech, Inc., Norcross, GA 30092.