Analysis of Solder Paste scooping with hierarchical point processes

In this paper we introduce a probabilistic approach for optical quality checking of Solder Pastes (SP) in Printed Circuit Boards (PCB). Dealing with unregistered image inputs, the task is to address at the same time SP identification, and detecting special soldering errors, called scooping. For this reason we introduce a novel Hierarchical Marked Point Process (HMPP) framework, which is able to handle the paste and scooping extraction problems simultaneously, so that the SPs and the included scoops have a parent-child relationship. A global optimization process attempts to find the optimal configuration of entities, considering the observed data, prior knowledge, and interactions between the neighboring circuit elements. The proposed method is evaluated on a real PCB image set containing more than 3000 SPs and 600 scooping artifacts.