Printed wiring board assembly, electrical device, and method for assembling printed wiring board assembly

An electrical device comprising:

• a printed wiring board assembly includes,
• a first board that includes a first surface,
• a second board that includes a second surface and faces the first surface,
• a plurality of first electrodes formed on a bottom surface of a recess, the recess being formed in one of the first surface and the second surface,
• a plurality of second electrodes formed on the one of the first surface and the second surface, the plurality of second electrodes being positioned outside the recess,
• a plurality of first solders each coupled to a respective one of the plurality of first electrodes, and
• a plurality of second solders each coupled to a respective one of the plurality of second electrodes,
• wherein the plurality of first electrodes are formed at a larger pitch than a pitch at which the plurality of second electrodes are formed, and a size of each the plurality of first solders is larger than a size of the second solders.

A method for assembling a printed wiring board assembly, the method comprising:

• providing a first board that includes a first surface;
• providing a second board that includes a second surface;
• performing a first forming or a second forming,
• the first forming including,
• forming a recess in the first surface,
• forming a plurality of first electrodes on a bottom surface of the recess,
• forming a plurality of second electrodes on the first surface, the plurality of second electrodes configured to be positioned outside the recess, the plurality of first electrodes configured to be formed at a larger pitch than a pitch at which the plurality of second electrodes are formed, and
• forming a plurality of third electrodes and a plurality of fourth electrodes on the second surface, the plurality of third electrodes configured to be formed at a larger pitch than a pitch at which the plurality of fourth electrodes, and
• the second forming includes,
• forming a recess in the second surface,
• forming a plurality of third electrodes on a bottom surface of the recess,
• forming a plurality of fourth electrodes on the second surface, the plurality of fourth electrodes configured to be positioned outside the recess, the plurality of third electrodes configured to be formed at a larger pitch than a pitch at which the plurality of fourth electrodes are formed;
• and
• forming a plurality of first solders each formed on a respective one of the plurality of third electrodes;
• forming a plurality of second solders each formed on a respective one of the plurality of fourth electrodes;
• positioning the first board and the second board such that the first surface of the first board faces the second surface of the second board;
• and
• performing a heating process to couple each of the plurality of first electrodes with a corresponding one of the plurality of first solders, each of the plurality of second electrodes with a corresponding one of the second plurality of solders, each of the plurality of first solders with a corresponding one of the plurality of third electrodes, and each of the plurality of second solders with a corresponding one of the plurality of fourth electrodes,
• wherein a size of each the plurality of first solders is larger than a size of the plurality of second solders.