PCB Design Glossary

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Bill of Materials

The bill of materials (B.O.M.) is an itemized list of parts and components that will be used in a design.  Each component will have a designator, a part number, supplier, etc....

Each BOM should be saved as a CSV, XLS, or XLSX file with no merged cells, no formulas, or other unusual formatting.  It is a good idea to have alternate part numbers on hand in case they are needed.

Blind Via

A blind via extends from an external layer of a PCB to an internal layer.  They are initially formed as through-holes vias that undergo an additional lamination cycle.

Three Types of Vias

From left-to-right, a through-hole via, a blind via, a buried via.


Circuits can be divided into blocks that have a particular function.  One benefit of this approach is that a functional block can be easily reused in future designs


Calf Path

One day through the primeval wood
A calf walked home as good calves should;
But made a trail all bent askew,
A crooked trail as all calves do.

Since then three hundred years have fled,
And I infer the calf is dead.
But still, he left behind his trail,
And thereby hangs my moral tale.
The trail was taken up the next day
By a lone dog that passed that way;
And then a wise bellwether sheep
Pursued the trail o’er hill and glade
Through those old woods, a path was made.

And many men wound in and out
And dodged and turned and bent about
And uttered words of righteous wrath
Because ’twas such a crooked path;
But still, they followed — do not laugh —
The first migration of that calf,
And through this winding woody-way stalked
Because he wobbled when he walked.

This forest path became a lane
That bent and turned and turned again;
This crooked lane became a road,
Where many a poor horse with his load
toiled on beneath the burning sun,
And traveled some three miles in one.
And thus a century and a half
They trod the footsteps of that calf.

The years passed on in swiftness fleet,
The road became a village street;
And thus, before we were aware,
A city’s crowded thoroughfare.
And soon the central street was this
Of a renowned metropolis;
And men two centuries and a half
Trod in the footsteps of that calf.

Each day a hundred thousand rout
Followed this zigzag calf about
And o’er his crooked journey went
The traffic of a continent.

A hundred thousand men were led
By one calf near three centuries dead.
They followed still his crooked way,
And lost one hundred years a day;
For thus such reverence is lent
To well-established precedent.

-- Sam Walter Foss


Capacitors connect two nets of different electric potentials with an electric field.  They can temporarily store energy in a small portion of a circuit.  While there is no direct electrical connection between the two nets, changes in one net will affect the other.


Parts that are shipped directly from a customer to an assembly house are said to be "consigned."  This method is often used for rare or hard-to-find parts.

Copper Weight

The thickness is of copper is measured in a variety of units depending on the region.  In America, for historical reasons, the thickness is measured in the pseudo-unit [ounces], which is short for [ounces]/[foot]².  Other regions measure it in [micrometers], while others measure in [grams]/[millimeter]².


The smallest circumscribed rectangle that surrounds a component body and land pattern.

Image from blogs.mentor.com

Cut tape

Integrated Circuits and Passive Components are shipped in a variety of packing options that make them easy to use with automated machinery.  One option is to place the components in either a paper or plastic housing that has sprocket holes along one edge.  The automated machinery uses the sprocket holes to feed the parts into the pick and place machine and index the location of parts.  When an entire reel of parts is purchased and fed into the machine, it is referred to as a reel.  When only a portion of that reel is purchased, the specified number of components will be counted off and cut away from the reel, leaving the customer with a cut tape.

SMT Feeder Bank

Above is a series of reels (left) and cut tapes (right) ready to be fed into an SMT machine.  Image from smtcaddy.com

The machines do have their limitations -- cut tapes cannot feed single parts, and a minimum tape length is required.  This leads to something manufacturers call overage.



The numbers specified in datasheets are usually only accurate in ideal, laboratory conditions.  And the real world is nothing like a laboratory.  So individual values will fluctuate with temperature, age, voltage, current, etc...

The process of adjusting the value down from the specified value is referred to as derating.  It is done by either looking at a graph, called a derating curve, or by following an equation.

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