Showing posts with label PCB. Show all posts
Showing posts with label PCB. Show all posts

PCB Board Styles

Most common board style
Solid construction, hard mounted to next assembly

Flexible circuits, typically used to replace cabling within a system

PCB Producibility

It is related to the difficulty of the design, and the particular printed board or printed board assembly.

Producibility Levels:

Level A – General Design Complexity - Preferred

Level B – Moderate Design Complexity - Standard

Level C – High Design Complexity – Reduced Producibility.

When appropriate this standard will provide three design producibility levels of features, tolerances, measurements, assembly, testing of completion or veriļ¬cation of the manufacturing processes that concerning progressive increases in sophistication of tooling, materials or processing and, accordingly advanced increases in fabrication cost.

PCB Technology

Analog PCB
 Typical functions are op-amps, voltage converters - power

Digital PCB
 Typical function is signal processing

 Function to produce radio frequencies, usually in the super high
Frequency Ranges:
 Low Frequency (LF) = 100 kHz
 Medium Frequency (MF) = 300-3000 kHz
 High Frequency (HF) = 3-30 MHz
 Very High Frequency (VHF) = 30-300 MHz
 Ultra High Frequency (UHF) = 300-3000 MHz
 Super High Frequency (SHF) = 3-30 GHz

PCB Assembly Classes

Class A – Through-hole mounted components only

Class B – Surface Mount components only

Class C – Simplistic through-hole and surface mount intermixed assembly

Class X – Complex intermixed assembly (Through-hole, surface mount, fine pitch and BGA)

Class Y – Complex intermixed assembly (Through-hole, surface mount, ultrafine pitch and chip scale)

Class Z – Complex intermixed assembly (Through-hole, ultrafine pitch, COB, flip-chip and TAB)

PCB Component Mounting

Automatic Insertion - Through-Hole Components
~ Board changes positions under insertion head
~ Dip Inserter
   Tube feeds DIPs into insertion head
~ Axial and Radial Inserter
   Components are sequenced and taped, then fed into lead former, then insertion head

Automatic Placement - Surface Mount Components
~  Board remains stationary
~  Chip Shooter
         For mounting chip components
 ~ Vacuum nozzle
         Selection and placement of larger components - ICs

Manual Placement
 ~ Unique and odd-form components formed and mounted by hand

PCB Solder Methods

Wave Soldering
- Through-Hole Assemblies
 Conveyed over wave of molten solder
 Cool Down

 - Surface Mount Assemblies
 Apply bind paint
 Component mounting
 Conveyed over wave of molten solder
 Cool Down

Reflow Soldering - Surface Mount Assemblies
 Apply solder paste
 Component mounting
 Solder reflow - Forced convection, Infrared
 Cool Down

Hand Soldering
 Used for temperature sensitive or odd-form components

PCB Features

Mechanical Outline
 Defines overall area for board design

 Board edge, mating area at next assembly

Mounting Holes
 Location, size, hardware used

Tooling Holes
 Used throughout fabrication, assembly and testing of boards

 Surface feature used for optical alignment of board during assembly

Keep-out Areas
 Areas where no components and/or copper can be located

Height Restrictions
 Areas where there are potential interference issues at next assembly

Fixed Component Location
 Connector locations for mating to next higher assembly
 Critical component locations

Additional Mechanical Hardware
 Card Guides, stiffeners, sockets

Design, Fabrication and Manufacturing constraints
 Board material
 Board thickness / Layer stack-up
 Via size
 Voltage and current used for circuits
 Critical circuit routing requirements
 Thermal considerations
 Fabrication and assembly methods

PCB Materials

FR4 - Flame Retardant 4
– Woven glass reinforcement with epoxy resin binder
– FR indicates it meets UL requirements for flame resistance

– Polytetrafluoroethylene (Teflon)

– Woven glass reinforcement with ceramic filled thermoset

Polyimide Film
– Epoxy resin system without

Introduction to PCB: Printed Circuit Board

Printed Circuit Boards are primarily an insulating material used as base, into which conductive strips are printed.

The base material is generally fiberglass, and the conductive connections are generally copper and are made through an etching process

The main PCB board is called the motherboard, the smaller attachment PCB boards are called daughter boards or daughter cards

PCB board design defines the electrical pathways between components

It is derived from a schematic representation of the circuit

When it is derived, or imported from a schematic design, it translates the schematic symbols and libraries into physical components and connections.

A PCB design package allows the designer to define and design on multiple layers

Printed Circuit Board Type

Types of PCB:

Type 1 – Single Sided PCB

Type 2 – Double sided PCB

Type 3 – Multilayer without Blind or Buried vias

Type 4 – Multilayer With Blind and/or Buried vias

Type 5 – Multilayer Metal Core board without blind and/or buried vias

Type 6 – MultiLayer Metal Core board with blind and/or buried vias

HASL - Hot Air Solder Level

It is a molten solder immersion and hot air leveling or blasting of surfaces and holes to provide a "retained" coating on exposed copper surfaces.

The advantage of HASL is excellent solderability, because as its name implies "Nothing solders better than solder."  One of the less-expensive surfaces finished with a good shelf life.

However, the problem with this finish is its limitation and difficulty. A limited capability on high density boards and a capacity to clear vias holes on a greater than 6:1 aspect ratio. A difficulty to maintain hole size tolerance along plated edges and to process thin material.