6 Key Considerations When Starting a New PCB Design

How often have you said to yourself, "I wish I would have known that earlier!" It's a fact that hundreds of decisions need to be made when starting a PCB design. The real struggle is which decisions need to be made first. A missed (or wrong) choice is similar to casting concrete. Once it's poured and cured, there isn't much that can be changed without a jackhammer. Many PCB designs have often been delayed or scrapped because of an overlooked decision.

This webinar will cover 6 key considerations that need to be made before starting any new PCB design:

1. Fabrication

2. Electrical

3. Mechanical

4. Regulatory

5. Procurement

6. DFM / DFT (Design for Manufacturing; Design for Test)

A cautionary note was brought to our attention regarding the bypass capacitors. "Usually generosity with bypass caps is a great thing, but beware LDOs as most go unstable if you go beyond the specified capacitance in the datasheet. There are a few out there that are stable at any capacitance." One example comes from Analog Devices: https://www.analog.com/media/en/news-marketing-collateral/solutions-bulletins-brochures/257253984LDO.Family.bulletin.pdf

One cannot go by a universal 15% rule of thumb because speed depends on the Dk.

Even if the Dk is the same for all dielectrics involved, a single rule of thumb cannot be created because one must account for the ratio of air and solder mask material creating an "Effective Dk."

You can see below the effect of the dielectric's Dk getting closer to air:

       For a Dk = 4.6, the stripline would be 182 ps/in
       Microstrip would be 144 ps/in, a speed increase of 20.88%
       Embedded microstrip would be 168 ps/in, a speed increase of 7.68%

       For a Dk = 3.3, the stripline would be 154ps/in
       Microstrip would be 127 ps/in, a speed increase of 30.22%
       Embedded microstrip would be 142ps/in, a speed increase of 21.98%

Also, the microstrip geometry will need to be adjusted for impedance, which depends on Dk.

The Saturn Electronics website provides equation-based calculators. One can get good approximations, which is far better than a universal rule of thumb.

6 Key Considerations When Starting a New PCB Design

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