Comma

Use a comma (,) to enhance readability or avoid ambiguity. Specifically, commas are used in the following cases:

Separate long, independent clauses (clauses that could stand alone as complete sentences) when the clauses are joined by and, but, or, yet, and for. Place the comma before the conjunction.

The U.S. has a position of perceived inferiority in PVD technology, and major U.S. semiconductor manufacturers are purchasing Japanese equipment.
Separate two adjectives that modify the same noun (the comma serves the same purpose as and).

highly trained, competent technicians
15, 5-second segments.
Separate an introductory phrase from the main body of the sentence.

In summary, the...
Set off nonrestrictive phrases (a phrase that is inserted to explain or modify a thought but is not essential to the meaning of the sentence).

The SEMATECH cleanroom, completed in 32 weeks, is a world-class facility.

The next technology node, which will focus on even smaller geometries, meets stringent specifications.
Set off interjections, transitional adverbs, parenthetical elements, and similar elements.

The model will become a flexible tool for cost analysis, thus increasing emphasis on the need for...
Separate items in a series. In some series, the elements' relationship might otherwise be confusing, so always use a comma before the conjunction that joins the last item in the series.

...practices, procedures and controls, and results data.

A comma is placed inside quotation marks but outside parentheses and brackets.

...in the fabrication sequence (e.g., on subsequent generations of DRAM devices), this is accomplished by...

Do not use a comma to separate compound verbs that share the same subject.

SEMATECH brings together the resources of industries, government, and universities and creates the synergy needed to meet the challenges ahead.