Flipping cards to face camera at weird angles

My 3D math is not so fresh these days (too much work in 2D games.)

I have a memory matching game in which the player flips cards to find matches. I recently reverted the camera from Orthographic to Perspective. I rotate the card with this function

float rotateRate = 180; transform.localEulerAngles = new Vector3 (0, rot, (-defaultZRotation * time) / animationTime);

The card will flip to face 180, but depending on it's position on the screen from the camera, that angle sets the cards to face a little off from directly looking at the camera.

What do I need to add to get this to face the camera and look like it is lying flat on the game board?