A fixture for fabricating a detector mini-module includes a lower block having a Y-datum lower block upper surface, an X-datum lower block surface, and a Z-datum lower block surface orthogonal to both the Y-datum lower and X-datum block surface surfaces. A mount block for a detector is positionable and in contact with the X-datum lower block surface, the Y-datum lower block upper surface, and the Z-datum lower block surface. An intermediate block is positionable on the lower block having an aperture passing through an upper surface and having an X-datum intermediate block surface and a Z-datum intermediate block surface. When a mount block for the detector mini-module is positioned on the lower block, the mount block is biased having an X-axis mount block planar surface aligned with the X-datum lower block surface, and biased having a Z-axis mount block planar surface aligned with the Z-datum lower block surface.