A liquid cooling system for an electronic board comprising a substrate, a plurality of electronic components (22, 23) secured to said substrate broken down into low-level and mid-level electronic components and into high-level electronic components, said system comprising: • a cold plate having external dimensions substantially equal to those of said substrate of the electronic board such that it covers the entire substrate and said low-level and mid-level electronic components, said cold plate being a plate made from a heat conducting material and comprising a primary cooling circuit with main channels inside which a heat transfer fluid flows, the supply of heat transfer fluid in said cold plate being done via an inlet connector and the exit of said heat transfer fluid from the cold plate being done via an outlet connector, • a plurality of heat sinks each comprising a main heat exchange zone able to bear against a high-level electronic component, said liquid cooling system being characterized in that it further includes a secondary circuit of flexible secondary channels connected to the main channels of the primary circuit by angled connectors secured in said cold plate, and in that said heat sinks are single-phase heat sinks which each comprise: ▪ a cooling block made from a heat conducting material comprising a lower part making up the main heat exchange zone, an intermediate part called the distribution part and an upper part connected to the cold plate, ▪ an inlet channel and an outlet channel which are connected on the one hand to the upper part of said cooling block respectively by means of an inlet connector and of an outlet connector, and on the other hand to a flexible secondary channel of the secondary circuit via an angled connector (1223, 1224), such that said cooling block is supplied by said heat transfer fluid flowing in said cold plate, said angled connectors (1223, 1224) being able to allow the rotation of said inlet and outlet channels (3, 4) relative to said flexible secondary channel to which they are connected, and in that the cooling block further comprises: ▪ a through slot located in the intermediate part to uniformly distribute the flow of said heat transfer fluid coming from the upper part in the form of a centered jet toward ▪ a support plate located in the main heat exchange zone and including a hollow central part with a zone provided with fins in order to generate turbulence in the flow state of said heat transfer fluid and a zone peripheral to said zone provided with fins to collect the heat transfer fluid and orient it toward said outlet connector. • a cold plate having external dimensions substantially equal to those of said substrate of the electronic board such that it covers the entire substrate and said low-level and mid-level electronic components, said cold plate being a plate made from a heat conducting material and comprising a primary cooling circuit with main channels inside which a heat transfer fluid flows, the supply of heat transfer fluid in said cold plate being done via an inlet connector and the exit of said heat transfer fluid from the cold plate being done via an outlet connector, • a plurality of heat sinks each comprising a main heat exchange zone able to bear against a high-level electronic component, ▪ a cooling block made from a heat conducting material comprising a lower part making up the main heat exchange zone, an intermediate part called the distribution part and an upper part connected to the cold plate, ▪ an inlet channel and an outlet channel which are connected on the one hand to the upper part of said cooling block respectively by means of an inlet connector and of an outlet connector, and on the other hand to a flexible secondary channel of the secondary circuit via an angled connector (1223, 1224), such that said cooling block is supplied by said heat transfer fluid flowing in said cold plate, said angled connectors (1223, 1224) being able to allow the rotation of said inlet and outlet channels (3, 4) relative to said flexible secondary channel to which they are connected, and ▪ a through slot located in the intermediate part to uniformly distribute the flow of said heat transfer fluid coming from the upper part in the form of a centered jet toward ▪ a support plate located in the main heat exchange zone and including a hollow central part with a zone provided with fins in order to generate turbulence in the flow state of said heat transfer fluid and a zone peripheral to said zone provided with fins to collect the heat transfer fluid and orient it toward said outlet connector.