In response to miniaturization, low-cost, and integrated transmit/receive (T/R) module demands, a millimeter-wave frontend module operating in the frequency range of 30-40 GHz was studied. A high-temperature co-fired ceramic (HTCC) substrate and ball grid array (BGA) packaging were adopted to achieve high-density integration of four transceiver channels for functions such as signal amplification, power distribution, and amplitude-phase control. Through the simulation and optimization of the vertical interconnection structure of the millimeter-wave signal in this module, low-loss signal transmission of this structure in the millimeter-wave frequency band was realized. Moreover, a printed circuit board (PCB) was designed and fabricated to test and verify this vertical interconnection structure. After calculations, the maximum insertion loss of the vertical interconnection structure was 0.78 dB. Using this vertical interconnection structure for millimeter-wave signals, a Ka-band four-channel millimeter-wave frontend module was fabricated. The test results show that in the frequency range of 30-40 GHz, the single-channel transmission power of this module was greater than 20 dBm; the receiving gain was greater than 21.33 dB; and the voltage standing wave ratio was better than 1.51, fulfilling the application requirements of the radio-frequency system.