A plate and fin type heat exchanger has a heat exchanger core made from a plurality of stacked, alternating first and second heat exchange plates of a generally inverted, U-shaped cross-section. Each plate has a top wall, closed peripheral sidewalls and open ends, and the open ends of the first plates are oriented at 90° to the open ends of the second plates. The sidewalls of the plates have end portions, which in adjacent plates, are aligned to form corners of the heat exchanger core. Opposed U-shaped manifold bodies are provided having open ends and lateral walls joined in a fluid tight manner to the aligned plate sidewall end portions. End plates close off the open ends of the U-shaped bodies to form manifolds. The corners formed by the aligned plate sidewall end portions allow for an improved connection between the heat exchanger core and the U-shaped manifold bodies. This helps to ensure that a fluid tight seal is created between the heat exchanger core and the manifold bodies when the components are joined together.