Thin film resistors and thick film resistors are characterized by a resistive layer on a ceramic base. Although their appearance might be very similar, their properties and manufacturing process are very different. The naming originates from the different layer thicknesses. Thin film has a thickness in the order of 0.1 micrometer or smaller, while thick film is around thousands time thicker. However, the main difference is method the resistive film is applied onto the substrate. Thin film resistors have a metallic film that is vacuum deposited on an insulating substrate. Thick film resistors are produced by firing a special paste onto the substrate. The paste is a mixture of glass and metal oxides.
The shape and size of surface mount resistors are standardized, most manufacturers use the JEDEC standards. The size of SMD resistors is indicated by a numerical code, such as 0603. This code contains the width and height of the package. So in the example of 0603 Imperial code, this indicates a length of 0.060″ and a width of 0.030″. This code can be given in Imperial or Metric units, in general the Imperial code is used more often to indicate the package size. On the contrary in modern PCB design metric units (mm) are more often used, this can be confusing. In general you can assume the code is in imperial units, but the dimensions used are in mm. The SMD resistor size depends mainly on the required power rating. The following table lists the dimensions and specifications of commonly used surface mount packages.
