A connector (100) includes an insulative housing (1) having a pair of side walls (10) with a central slot (11) formed therebetween, a set of terminals (5) including first terminals (51) and second terminals (52) and a spacer (3). Each side wall has a set of passageways (12). Each first terminal has a first contacting portion (511) protruding into the central slot, a first tail portion (513) mounted on a PCB, and a first connecting portion (512). The first connecting portions and the first tail portions are arranged in two rows. Each second terminal has a second contacting portion (521) protruding into the central slot, a second tail portion (523) mounted on the PCB, and a second connecting portion (522). The second connecting portions and the second tail portions are arranged in another two rows. The spacer (3) has a set of first protrusions (31) and forms a plurality of first grooves (32) located between each two adjacent first protrusions. The first protrusions each has a second groove (33) formed thereon. The spacer defines a set of second protrusions (34) and forms a plurality of third grooves (35) located between each two adjacent second protrusions (34). The second protrusions each has a fourth groove (36) formed thereon.