Manufacturing method of common mode filter

A manufacturing method of common mode filters comprising the steps of:

• Step A:
• manufacturing a composite substrate that includes a base layer, an adhesive layer over the base layer, and a first magnetic material layer coated over the adhesive layer;
• the base layer and the first magnetic material layer sintered and connected by the adhesive layer so as to form the composite substrate;
• a particle size of magnetic material of the first magnetic material layer is smaller than 10 μm and a thickness of the first magnetic material layer ranges from 20 μm to 80 μm;
• Step B:
• forming a common mode choke layer over the composite substrate;
• the common mode choke layer having a plurality of inductive coils and a plurality of insulated layers while the inductive coil including at least a pair of leading-out terminals;
• a second magnetic material layer is coated over an upper surface of the common mode choke layer for forming a plurality of common mode filters on the same composite substrate;
• a particle size of magnetic material of the second magnetic material layer ranges from 34 μm to 80 μm and a thickness of the second magnetic material layer is about 50 μm to 150 μm;
• Step C:
• performing a first cutting by means of a cutting tool to form a groove between two common mode filters;
• the cutting tool cuts the second magnetic material layer and the common mode choke layer so that the leading-out terminals are located on sides of the common mode choke layer;
• Step D:
• forming external electrodes in the groove by sputtering, lithography and electroplating sequentially and allowing the external electrodes connected to the leading-out terminals of the inductive coils;
• the external electrode extending to an upper surface of the second magnetic material layer so as to form a conductive part;
• and
• Step E:
• cutting the composite substrate along the groove by a cutting tool to complete production of a plurality of single common mode filters.