An SO DIMM connector includes an insulative housing (10) defining an elongated slot (12) along a longitudinal direction thereof. A plurality of passageways (14) are formed by two sides of the slot (12) in the housing (10). A plurality of contacts are received within the corresponding passageways with contact portions extending into the slot (12). A pair of supporting platform (16) are formed at two opposite ends of the housing (10). A pair of latch devices (22) are disposed on the corresponding supporting platforms (16), respectively. Each latch device (22) includes a plastic member (24) and a metal member (26) commonly deflectable with regard to the housing (10). A substrate module (100) is inserted into the slot (12). The module (100) defines a pair of notches (101) in two side portions and a pair of grounding pads (102, 106) respectively on both surfaces (104, 108) thereof around each of said notches (101). The plastic member (24) defines a locking protrusion (28) and a restriction protrusion (30) respectively abutting against the upper surface (104) and received within the notch (101) of the module (100), while the metal member (26) defines a pair of grounding tangs (44, 46) respectively engaged with the corresponding grounding pads (102, 106) on two opposite surfaces (104, 108) of the module (100).