Printed Circuit Boards
Written by a world-renowned electronics expert, this reader-friendly guide helps engineers and technicians solve issues in PCB layout, fabrication, assembly, and testing.
TABLE OF CONTENTS Printed Circuit Boards
13.3: Soldering Variables
13.3 Soldering Variables
The important variables of soldering are: temperature, time, tarnish-free surface, right flux and right solder. These variables are important to all the soldering techniques and should be always kept in mind. For achieving good results the golden rule is "Applying the right temperature to the solder as well as to the lands/terminations to be soldered for the correct time on a clean surface by using the right flux and proper solder will provide excellent joint looking bright and shiny".
13.3.1 Temperature and Time Taken for Soldering
The temperature and the time of heat application determine the thickness of the inter-metallic compound. Because of the brirtleness of the inter-metallic layer, a too thick layer may cause solder cracking under conditions of thermal or mechanical stress. Beside, the larger thickness of the inter-metallic compound, excess of heat and its longer application may also destroy heat-sensitive components as well as the board. The aim is to keep the temperature low and the time of the highest heat application as short as possible. For surface mounted components, the shear strength is very critical. Due to the different thermal expansion coefficients of the board and components, temperature changes lead to different changes in length and the creation of shear forces especially for larger components.
The temperature for soldering depends on the melting point of solder and its application. For each metal and solder combination, there is a critical temperature below which wetting does not occur or take place to a very small...
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