Printed circuit board
Plated through-hole technology and its use in multi-layer PCBs were patented by the U.S. firm Hazeltine in 1961. This allowed much more complex boards, with components placed closely together. Integrated circuit chips were introduced in the 1970s, and these components were quickly incorporated into printed circuit board design and manufacturing techniques. Today the Printed Circuit Board can have up to100 layers in some applications.