How to apply underfill adhesive dispensing to the bottom of chips on a PCB board?
Underfilling chips on PCB boards is a precision process primarily used for chips with ball grid arrays on their undersides, such as BGAs (Ball Grid Arrays) and CSPs (Chip-Scale Packages). Below, I will explain the procedure in detail, covering its purpose, materials, equipment, steps, and precautions. I. Why Use Underfill? The primary purpose is to enhance the mechanical strength and long-term reliability of chips, especially in products operating under harsh conditions. 1. Resist Mechanical Stress: Prevents solder joint cracking caused by PCB bending, vibration, or impact. Underfill is critical for portable devices like smartphones during drops. 2. Mitigating Thermal Stress: Chips and PCB substrates (typically FR-4) have differing coefficients of thermal expansion (CTE). During thermal cycling, this mismatch generates stresses that cause solder joint fatigue failure. Underfill material evenly distributes these stresses, protecting solder ...