The term process window is used to define your reflow spec in relation to your process. Vitor Barros of KIC Europe has used the following analogy to describe this relationship.
The following example describes when you have a reflow process that does not fit your product’s specification. You cannot change your process but you change change your spec (get a bigger picture frame).
The other extreme is where your spec is fixed and you need to modify your process (the picture canvass).
When both fit, you have what would be expected, a picture that fits perfectly to its frame.
I discuss with Vitor Barros of KIC Europe the Process Window.