An important progress is the development of wire winding technology. At each connection point, a small size wire is wound on a column to form a highly durable and easily replaceable air tight connection.
As electronic products shift from vacuum tubes and relays to silicon and integrated circuits, the size and cost of electronic components begin to decline. Electronic products are more and more popular in consumer goods. The pressure of reducing the size and manufacturing cost of electronic products urges manufacturers to find better solutions. So the printed circuit board was born.
A PCB is a bit like a cake or lasagna – there are alternate layers of different materials that are laminated together by heating and adhesive, resulting in a single object.
FR4 type
The substrate material is usually glass fiber. Historically, the most common code name for this kind of glass fiber is FR4. This solid core gives PCB rigidity and thickness. There are also flexible PCBs built on flexible high temperature plastic (Kapton or equivalent).
You will find many printed circuit boards of different thicknesses; The most common thickness of sparkfun products is 1.6 mm (0.063 “). Some of our products – lilypad boards and arudino Pro miniboards – use 0.8 mm thick boards.
Cheaper printed circuit boards and performance boards will be compared with other materials, such as epoxy or phenolic resin, lacking durability of FR4, but much cheaper. When you solder to a PCB, you’ll know that you’re using this type of PCB – they have an obvious odor. These types of substrates are also commonly found in low-end consumer electronics products. Phenolic resin has low thermal decomposition temperature. When the soldering iron stays on the board for too long, it will cause delamination, smoking and carbonization.
The next layer is thin copper foil, which is laminated onto the circuit board with heat and adhesive. On a common double-sided printed circuit board, copper is coated on both sides of the substrate. In low-cost electronic products, one side of PCB may only be copper. When we talk about double-sided or double-layer board, we mean the number of copper layers in the lasagna (2). This can be as little as 1 layer or as many as 16 layers or more.
The thickness of copper can vary and is specified by weight in ounces per square foot. Most PCBs contain one ounce of copper per square foot, but some PCBs with very high processing power may use two or three ounces of copper. Each ounce per square is converted to about 35 microns or 1.4 thousandths of an inch of copper thickness.
The top layer of copper foil is called tin coating. This layer provides the PCB with green (or red in sparkfun). It is covered on the copper layer to make the copper trace come into accidental contact with other metals, solders or conductive drills. This layer helps the user weld to the correct position and prevents solder jumpers.
In the following example, a green solder mask is applied to most of the PCB, covering small traces, but leaving silver rings and SMD pads exposed so that they can be soldered to.