An electronic circuit assembly includes an interposer substrate, a wiring substrate, an electrical connective part and an electronic component. The interposer substrate with a first coefficient of thermal expansion (CTE) includes a first surface, a second surface opposite to the first surface, and a first side surface connecting to the first surface and the second surface. The wiring substrate with a second CTE is disposed below the second surface. The first CTE is lower than the second CTE. The electrical connective part is disposed in the interposer substrate and extends to the first side surface. The electronic component is attached to the first side surface and is electrically connected to the electrical connective part.