PCB Design Glossary

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A schematic is a pictorial representation of circuit components and their connections.  Symbols used in a schematic can vary depending on the convention used and a designers preferences.


Serial Clock Line is the synchronous timing line on the I2C data bus.


Serial Data is the data transmission part of the I²C data bus.


Slash-sheets are dielectric material specifications sheets detailed in an appendix to IPC-4101.  The pages provide material specifications, such as coefficient of thermal expansion, glass transition temperature, resin content, glass type, etc...

Material vendors such as DuPont, Isola, Rogers, etc... create cores that satisfy particular requirements, for example /28 or /41.  PCB engineers that specifically require Isola-370HR might pay more than an engineer that simply request a material that satisfies /98 or /99, since a manufacturer might have a similar product on hand from a different manufacturer.


Pure substances undergo phase changes at specific temperatures.  Mixtures undergo phase changes over a range of temperatures.  Solidus is the temperature at which solids begin to form in a cooling mixture.  

Solder Phases


The process of selecting and presenting data about a part in a favorable, and often inconsistent way.  This tends to give engineers false impressions about the performance of a product. 

There are companies that purchase products from all manufacturers in a product class and independently test multiple samples in a controlled environment.  These companies then sell their results to engineers.  

Hard Way Hughes

"Specmanship is looked down upon by engineers as it can lead to costly mistakes.  I know of several engineers that will stop using parts from companies they believe are manipulating datasheet data.  Here's an example from two real companies (names redacted, and data changed) I talked to at Sensor Expo last year when I was trying to select a gyroscope for a project.


Company A markets a gyroscope with a bias instability of 0.4 °/hr.  Company B markets a gyroscope with a bias instability of 1.4 °/hr.

You'd choose company A, right?

Hold on -- company B suggested that I request the bias instability over the entire temperature operating range for product A.

Specmanship Example

What isn't presented in marketing materials is that when the gyroscopes were characterized over the entire operating temperature range of -55° C to 125°C, company A chose to present the best number, while company B chose to present the worst-case scenario."


A Serial Peripheral Interface is a data bus that transfers data between two or more integrated circuits.

It has the benefits of high speed and full-duplex communication.