Week #13: Electronic Components, Labelling & Surface Mount Components

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rjagodowski
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Joined: Fri Sep 04, 2015 6:59 pm

Week #13: Electronic Components, Labelling & Surface Mount Components

Post by rjagodowski »

Before starting this material, we will look at some Surface Mount content posted in Week #13 of EET-255.


You were sent an email (last week) with access to various videos which support this content. Two of the videos about soldering & surface mount soldering should definitely be viewed. I would recommend watching the others or downloading them for later viewing.


Here's information about the Complete Resistor Color Code. Your experience has probably mostly been with what are known as 4-band resistors (2 significant digit bands, 1 multiplier band & 1 tolerance band) These were typically used for resistors which had either 20%, 10% or 5% tolerances.

There are other color banding schemes that are in use with which you should be familiar. There are 3 band resistors (2 significant digit bands & 1 multiplier band, tolerance was 20%). These are not too common any more, but you may see them if you ever look at vintage circuits from the 1960's and before.

More commonly now are "precision resistors" with tolerances of 2%, 1%, 0.5%, 0.25%, 0.1% and even 0.05%. In order to be able to specify the required significant digits for these types of resistors, additional color bands are added. Here's a chart which shows how the color code adapts to the various tolerance resistors:
Color Code Table for 3-6 Band Resistors.png
Color Code Table for 3-6 Band Resistors.png (180.97 KiB) Viewed 1717 times




Here's a bit about Resistor Temperature Coefficients.


The "E-Series" designation is used for each tolerance specification. The number after the "E-" specifies how many different component values exist within each decade of range. For example, E-3 only has 3 values per decade: 1, 2.2, 4.7, typically used either when exact values don't really matter (such as pull-up/pull-down resistors) or back when component manufacturing tolerances were about 50%. More common is E-12 for 10% tolerance and E-24 used for 5% tolerance. See the chart below.
E-12 and E-24 Series.png
E-12 and E-24 Series.png (28.62 KiB) Viewed 1715 times

The banded color code scheme worked well, especially back in the days before printed circuit boards were used and the wiring was point-to-point. The bands allowed an assembly/technician to see the resistor's nominal value regardless of how the component was mounted. Here's a pic of what the inside of typical 1960's era television set looked like:
Point-to-Point component mounting - 1960's TV.png
Point-to-Point component mounting - 1960's TV.png (735.27 KiB) Viewed 1716 times
Obviously, the advent of the printer circuit board (PCB, or just PC) neatened things up quite a bit, and eventually it led to more "modular" construction where specific circuits were mounted on specific boards. A manufacturing technique still used today, although the amount of componentry and function when can be fit on a single board often precludes the necessity of multiple boards.


It should also be mentioned that there is also a Capacitor Color Code and an Inductor Color Code. Again, back in the day of point-to-point wiring, the "banded" color codes were used to ease the identification, installation and repair electrical and electronic circuits.

As manufacturing techniques began to improve it became increasingly common for the actual component values to be printed on the components directly. For PC mounted components this worked well as components were all viewed from the same basic perspective, the top of the circuit board.

The ever increasing desire to make products smaller & more reliable led to the development of Surface Mount Technology back in the 60's, pushed by the U.S. Space program and paralleled with the development of digital computers. Still, Surface Mount Technology (SMT or SMD (surface mount device)) had only impacted about 10% of the electronics market by the mid 1980's!

However, the small size of the SMD's required a new development to express the component values as many SMD components were too small and didn't provide sufficient area to imprint the component values.

Here's the codings & markings for surface mount resistors.

Another way of labelling components is known as the RKM Code. This technique originally was used in documentation as it had the advantage of not requiring the use of a decimal point to define a component's value. This is important because documents which are photo-copied or reproduced in various ways might either no copy the small decimal point, or perhaps a speck of dirt or copy imperfection might insert a decimal point where one shouldn't exit. Those scenarios are not possible using this system. It is now often seen printed on electronic components, instead of the other methods mentioned above.
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