Offline spray cleaning equipment is suitable for cleaning small to medium batches of PCBAs, similar to the working principle of a dishwasher. Circuit boards and components are placed in cleaning baskets, and the cleaning, rinsing, and drying processes are completed within the same chamber. Based on experience using dishwashers, components obscured by other items cannot be thoroughly cleaned. So, does a similar "shadowing effect" occur in offline spray cleaning?
In the following study, you will systematically understand various configurations of offline spray cleaning, gain insight into the background and scientific basis of the "shadowing effect" hypothesis, and review the rigorous testing system we designed to verify this issue.
I. Basic Concepts: What is the Shadowing Effect?
The more densely packed the components in an offline spray cleaning process, the higher the possibility of components overlapping each other—this phenomenon is called the "shadowing effect." Typically, components come into contact with the cleaning agent from above, below, or the sides. Therefore, the cleaning agent can never be sprayed from all directions and angles. Furthermore, some larger components on the PCBA may also cause shadows to appear in certain areas.
Simplified Schematic Diagram of Offline Spray Cleaning
This means that some areas on the components will always experience a shadowing effect, resulting in poor cleaning in these areas or requiring longer cleaning times to achieve good results.
II. Scientific Testing Scheme
To investigate whether a shadowing effect always exists when cleaning components using offline spray equipment, we selected cleaning systems with different configurations and conducted tests.
No-load Operation:
In the initial stage, only a few specially designed assembled glass plates coated with test flux were cleaned in each system. This allows the cleaning performance of the system to be determined without the risk of shadowing from other components.
No-load Operation: Only test plates are placed in the cleaning equipment.
Full-load Operation: Subsequently, glass test plates are reloaded at the original fixed positions in each system, and the cleaning basket gaps are fully loaded with standard components of the same specifications, thereby accurately reproducing the inducing conditions of potential shadowing effects.
Full-loaded components, test plate positions are the same as in no-load operation.
We compared the cleaning results below the components on the glass test plates during no-load operation with the results under full-load operation for each equipment.