PCB Design Glossary


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S

Slash-sheet

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.


Solidus

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


Specmanship

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.

Example:

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."


SPI

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.


T

Traveler

A traveler is a set of instructions that assembly line workers follow to construct a PCB.

Traveler


V

via

VIA stands for Vertical Interconnect Access.

Electrical connections between components are referred to as interconnects.  Traces and copper pours connect make in-plane (horizontal) connections, and formed cylinders called VIAs make the out-of-plane (vertical) connections.

Vias

This image was made by digitally removing all non-copper features from a printed circuit board.  From left to right, a buried via, a blind via, a through-hole via, stacked microvia, and staggered microvia.
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