disposed between the first fixing portion 325 and the supporting section 310 the second indentation 323 is disposed between the second fixing portion 321 and the supporting section 310 the first indentation 326 and the second indentation 323 at least partially accommodate the first bend portion 410 and the second bend portion 430 of the flexible printed circuit 400 respectively therefore the strength of the complex circuit board is improved due to the structural design moreover as shown in fig5 a to fig5 c to enhance the strength of the combining section 330 the first fixing portion 325 and the second fixing portion 321 can be rectangle wedge or arc shaped protrusions so that the flexible printed circuit 400 and the printed circuit board assembly 300 are prevented from being detached from each other the present invention also provides a fabrication method of the complex circuit board as shown in fig6 the step s 10 is forming a first fixing portion 325 on a connecting section 320 of a printed circuit board assembly 300 in another embodiment a second fixing portion 321 is further formed on the printed circuit board assembly 300 the step s 10 further includes forming a first indentation 326 and a second indentation 323 on one side of the first fixing portion 325 and the second fixing portion 321 respectively the step s 20 includes forming a first fixing hole 425 on a contacting section 420 of the flexible printed circuit 400 the first fixing hole 425 corresponds to the first fixing portion 325 in another embodiment a second fixing hole 421 is formed.