New-generation modular power supplies widely adopt integrated chip-scale molding technology, which integrates magnetic cores, active components, PCB substrates and epoxy molding compound into a single unit. This solution effectively shrinks package dimension, lowers overall weight and improves heat dissipation performance. Nevertheless, high integration density, heterogeneous multi-material interfaces and stringent requirements for high reliability and long service life pose critical challenges to molding processes. Low surface energy, poor wettability and weak interfacial adhesion between molding compound and diverse substrates including base material, solder mask ink and magnetic core easily trigger interfacial delamination, crack initiation and moisture ingress under combined stress from thermal cycling, mechanical vibration, temperature and humidity fluctuation. Such defects consequently lead to deteriorated insulation, parameter drift or even complete functional failure of power modules.

As a dry microscopic surface modification technology differing from conventional wet cleaning that only removes contaminants, plasma cleaning optimizes substrate interfacial conditions comprehensively via three effects: chemical cleaning, surface activation and nano-scale micro-roughening. It fundamentally eliminates molding delamination and fits diverse packaging processes of power modules.

Working Mechanism of Plasma Cleaning

1. Surface Cleaning

Oxygen plasma generates abundant high-energy active free radicals to oxidize and decompose organic contaminants such as residual flux and surface grease on substrates. Pollutants are decomposed into gaseous CO₂ and water vapor and fully evacuated by vacuum pump, leaving no residue, water stain or secondary pollution. The removal of surface barrier layer delivers a clean substrate surface for robust adhesion during molding.

2. Surface Activation

High-energy plasma breaks inert molecular bonds on substrate surfaces and introduces massive polar functional groups including hydroxyl and carboxyl groups, drastically lifting substrate surface energy.

3. Surface Roughening

Plasma etching modifies microscopic surface topography and increases surface roughness. Higher roughness enlarges specific surface area, improves hydrophilicity and water permeability of substrates, and expands contact area between base material and molding compound to strengthen mechanical interlocking adhesion.

Substrate Wettability after Plasma Treatment

Plasma modifies plastic surface properties and changes its wettability (shown in Figure 1). While adjusting surface energy and surface tension, plasma treatment optimizes substrate hydrophilicity as well as bonding performance and bonding strength.

Comparison of Effects Before and After Plasma Cleaning

Thermal shock tests were performed on encapsulated power modules with and without plasma cleaning, followed by ultrasonic C-Scan acoustic inspection after thermal cycling. Testing was carried out via an ultrasonic scanning microscope equipped with a 50 MHz intermediate-frequency probe under C-Scan mode, and the obtained acoustic scanning images are presented in Figure 2.

As shown in the test results: For power modules without plasma cleaning (Figure 2a), internal delamination inside the encapsulant accounts for a large proportion of the overall package. Specifically, the delamination area between the PCBA substrate and encapsulation resin occupies approximately 45% of the total packaging area, indicating severe interfacial delamination between molding compound and chips/substrate and severely compromised interfacial bonding integrity. In contrast, plasma-cleaned power modules (Figure 2b) feature drastically reduced delamination and substantially expanded intact bonding zones; the delamination ratio between PCBA substrate and encapsulant drops to roughly 6%, corresponding to a 39% reduction in delaminated area. This demonstrates fundamental improvements in interfacial adhesion and remarkable enhancement of thermal fatigue resistance as well as packaging reliability of the encapsulation interface.

An analysis on interfacial conditions of the two batches of modules is summarized as follows: Plasma-cleaned PCBA modules form robust interfacial bonding via mechanical interlocking from substrate surface micro-roughness and chemical bonding induced by polar functional groups, which efficiently dissipates thermal stress and avoids obvious interfacial delamination. Conversely, modules without plasma treatment only rely on weak physical adsorption between substrate and molding compound, failing to withstand cyclic thermal stress and resulting in visible interfacial delamination defects. The test verifies that plasma cleaning effectively improves the environmental stress resistance of encapsulated modules and guarantees packaging reliability.