J-Tech Engineering - Printed Circuit Board Design Expertise

Printed Circuit Board Design Expertise

By working closely with our customers to ensure all pertinent design criteria are met, J-Tech can produce world-class printed circuit board solutions. Some of the 'criteria' typically considered in a board layout are:

Is regulatory approval (FCC part 15A or 15B) required by this design? If so, many precautions must be taken to ensure that the design will not radiate noise at a level exceeding guidelines set by governing bodies.
Is safety approval critical? For instance, the PCB material employed may need to be of a self extinguishing nature.
Will the board be subject to static discharge? If so, precautions must be taken to protect the input stages from being destroyed in the course of normal operation.
Is there a telephony interface on the design? If the board must ultimately connect to the telephone network, the design must 'fail' safely in the presence of a line surge or lightning strike. The translation is that the board may not catch fire or leave the connection to the Central Office (CO) in an off-hook state.
How sensitive are any analogue inputs on the design? How much protection from the noisy digital world must be provided? This can lead to the use of:
- additional layers;
- split power/ground planes;
- filters between analogue and digital planes;
- electro-magnetic-interference (EMI) shielding (metal can);
- feedback controlled ovens to reference out the effects of temperature variation on amplifier stages (instrument amplifiers are a typical case).
Are there any high-current requirements in the design? If so, determine the average temperature rise through the copper traces during normal operation. For example, in the DC UPS design featured under examples, the circuit board can have in excess of 50 Amperes flowing through it during the initial stages of a power failure.
What physical limitations are imposed? For example:
- unique shape to fit into a custom enclosure;
- special placement requirements to meet height restrictions;
- mounting hole locations;
- additional space for temperature controlled ovens or metal covers for sensitive RF stages.
Are there any unusual requirements such as controlled impedances for high-speed data transmission lines? In this case, some traces will need to be laid out with impedance control procedures in place.
If there is a high layer count due to space restrictions, will any blind vias be required? If so, this can have a substantial impact on the cost of the final product. Sometimes a larger board is cheaper, even though more packaging is required. On the other hand, size can frequently be at the pinacle of the decision process.

Some illustrations of printed circuit board layouts are shown below. Each example depicts a different type of design expertise typically employed in our design process.

CPU layout example. A section of an alarm system.

A CPU layout from the core of an embedded monitoring system.

Above is shown a section of a CPU and surrounding connections. Most designs with pitch this fine will require at least four layers to route properly. Four layers is preferred in these cases as generally there are less problems with unintentional radiation of RF energy, or EMI. EMI is generally a problem where severe impedance mismatches occur, and extremely fast rise and fall times of digital signal lines are encountered. A specific example of a consistent problem in high-speed designs like the one shown above is that of clock oscillators used to drive the chip itself. Traces coming from oscillator drive pins should be kept as short as possible, filtered (again, if possible), and kept as far from other traces as is reasonable.

RF Input Stage.

At left is shown a portion of an RF input stage for an embedded servo controller. In the case of RF input and drive stages, a well drawn schematic can be invaluable in determining what is important in the layout. Generally, these types of stages are linear in nature, meaning not that there are second or higher order effects taking place on transmission lines, but that the components are laid out in stages, each one feeding into the next. This means components can be oriented such that traces are as physically short as possible and use few, if any, vias. This can give some designs the appearance of being all components and copper planes, with very little in the way of visible traces. In the RF stage shown at left, the antenna connection to the design (the outermost pin in the upper left corner) passes through a filter stage and into a discrete amplifier. Most traces are shorter than the components themselves.

J-Tech Engineering would be pleased and interested to discuss any special layout requirements for your designs. We enjoy partnering closely with our customers to produce the most effective designs possible. Our customers' successes are viewed as our successes. Please see the company information page for contact information.

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