Component Creation

Good Circuit Boards require good land patterns and good schematics require good components.

1. Introduction

Every part on every schematic is represented by a schematic symbol.  You are likely already familiar with most schematic symbols such as the capacitor, resistors, diodes, and even integrated circuits.

Delta Sigma Schematic

While there are some standards documents (such as IPC-2612-2010) that cover recommended schematic symbols and diagram creation -- there is still a great deal variation in the industry -- all of it relatively minor.

The flow of your schematic will likely be from left to right, top to bottom.  So signal inputs will be on the left side and signal outputs will be on the right side of a component.  If you need to, you can always rotate and flip the component when you are ready to place it in your schematic

Consistency

It is more important to be consistent in your documentation than to follow a particular standard.  An engineer that sees a zig-zag resistor will recognize it as such.  An engineer that sees a rectangular resistor will recognize it as such.  But an engineer that sees zig-zag resistors on page one followed by rectangular resistors on page two is going to be terribly confused. 

Follow the guidelines established by your company, or if you are a new/independent designer, perhaps consider IPC-2612 guidelines.  Absent either of those options, maintain the conventions established by your EDA program.  That means you should maintain the default resistor style, the default capacitor style, etc...

Pins

This week, we will make schematic components with pins that represent the pads from land patterns.  Each component pin represents a different pad and the component pins will be connected to signal lines, power rails, and ground planes in our schematic document.

Pins are Connected to Pads

Left:  The RTC component used in our schematic.  Right:  The RTC Land Pattern

Grid Setup

Land patterns are designed using metric measurements.  Component symbols are designed using imperial measurements.  When creating your component pins, align them along a square grid with 0.1" (2.54 mm) spacing in both the x and y directions.  If the component is small, and space permits on your diagram, you can spread the component pins even further out (0.2", 0.3", 0.4") as long as the spacing is in 0.1" increments.

Pin Grid on 0.1" centers

Procedure

The basic procedure we'll follow is this:

  • Find or Create the Land Pattern (Done)
  • Find or Create the Component
  • Attach Component Pins to Land Pattern Pads
  • Save Component to Library

Hard Way HughesYou do not need to do extra work this week.  Many of the component diagrams should already exist in your library and you can just copy them over.  Make enough unique components that you feel that you've got the hang of it and then copy the rest or borrow from coursemates.