Printed circuit boards can be single-sided (one layer of copper), double-sided (two layers of copper on either side of a single layer of substrate), quad-sided and multilayer.
Multilayer PCBs significantly increase the density of component placement. The rise in popularity of multilayer PCBs with more than two and especially more than four copper planes occurred simultaneously with the introduction of surface mount technology. However, multilayer PCBs make circuit repair, analysis, and modification much more difficult.
One of the easiest boards to manufacture is the two-layer board. It has copper on both sides, which are called outer layers. After two-layer circuit boards, the next step is the four-layer board. A four-layer board adds significantly more routing capabilities in the inner layers compared to a two-layer board, and often a portion of the inner layers is used as a ground or power plane to achieve better signal integrity, higher signal transmission frequencies, lower electromagnetic interference, and better power supply decoupling.
In multilayer boards, layers of material are laminated to each other in an alternating sandwich: copper, substrate, copper, substrate, copper, substrate, copper, etc. Each plane of copper is etched, and all internal holes (which will not extend to both outer surfaces of the finished multilayer board) are melted through before the layers are laminated together. Only the outer layers need to be coated, the inner copper layers are protected by the adjacent substrate layers.
One of the easiest boards to manufacture is the two-layer board. It has copper on both sides, which are called outer layers. After two-layer circuit boards, the next step is the four-layer board. A four-layer board adds significantly more routing capabilities in the inner layers compared to a two-layer board, and often a portion of the inner layers is used as a ground or power plane to achieve better signal integrity, higher signal transmission frequencies, lower electromagnetic interference, and better power supply decoupling.
In multilayer boards, layers of material are laminated to each other in an alternating sandwich: copper, substrate, copper, substrate, copper, substrate, copper, etc. Each plane of copper is etched, and all internal holes (which will not extend to both outer surfaces of the finished multilayer board) are melted through before the layers are laminated together. Only the outer layers need to be coated, the inner copper layers are protected by the adjacent substrate layers.