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18 SMT007 MAGAZINE I JUNE 2026 The Challenge of Cleaning Highly Dense Assemblies Because of limited access beneath components, bottom-terminated components (BTCs) such as QFNs, LGAs, and microBGAs, create some of the most challenging cleaning environments in electronics manufacturing. With standoff gaps frequently below 100 µm and often less than 2 mils, flux residues can completely flood the cavities beneath these components, restricting outgassing pathways and trapping contamination beneath the termination. The cleaning process beneath low-standoff com- ponents follows several sequential steps: 1. Wet the residue. 2. Soften residue into a gel-like state. 3. Dissolve the residue. 4. Establish flow channels beneath the compo- nent for residue removal. Removing these residues requires significantly more than chemical solvency alone. Effective cleaning depends on high-energy spray impinge- ment, optimized nozzle geometry, proper fluid dy- namics, and sufficient chemistry exchange beneath the component. Not all cleaning systems can deliver the required energy transfer. Achieving this requires careful optimization of nozzle design, spray angle, flow rate, orifice geometry, and spray distance. The effectiveness of the process depends on how efficiently fresh cleaning chemistry reaches the dissolution site and removes saturated chemistry from beneath the component. This becomes particularly critical for larger bottom-terminated packages. Direct Spray vs. Tangential Spray Systems To maximize energy transfer beneath components and minimize spray shadowing from neighboring devices, direct spray systems have demonstrated superior cleaning performance in many high-densi- ty applications. In direct spray systems: • Spray beams create omnidirectional flow along the board surface • Fluid flow is optimized for penetration be- neath components • Bidirectional scanning improves cleaning uniformity across the assembly Figure 2: Different designs of spray kinematics in cleaning machines for electronic assemblies. Figure 3: Direct spray against the surface.