The first PCBs used through-hole technology, mounting electronic components by leads inserted through holes on one side of the board and soldered onto copper traces on the other side. Boards may be single-sided, with an unplated component side, or more compact double-sided boards, with components soldered on both sides. Horizontal installation of through-hole parts with two axial leads (such as resistors, capacitors, and diodes) is done by bending the leads 90 degrees in the same direction, inserting the part in the board (often bending leads located on the back of the board in opposite directions to improve the part's mechanical strength), soldering the leads, and trimming off the ends. Leads may be soldered either manually or by a wave soldering machine. COUNT 5
QSN1 If a lead wasn't soldered manually, what device was used? ANS1 wave soldering machine QSN2 Which type of PCB construction technique was used first? ANS2 through-hole QSN3 In through-hole construction, what are the leads on the front attached to on the back? ANS3 copper traces QSN4 For boards with two sides, to what angle are leads bent to in order to install them horizontally? ANS4 90 degrees QSN5 What is improved by bending leads in opposite directions on the back of double-sided PCBs? ANS5 mechanical strength