PCBA chip mounting (also called die mounting or component placement) is a precision manufacturing process that attaches integrated circuits (ICs, or “chips”) to the PCB, forming the core of the PCBA’s functionality. Unlike manual soldering for through-hole components, chip mounting relies on automated equipment (Surface Mount Technology, SMT) to handle miniaturized chips (e.g., QFP, BGA, QFN packages) with submillimeter pitch—ensuring accurate alignment, consistent solder joints, and high production efficiency. Improper mounting can lead to critical failures: misaligned chips cause open circuits, insufficient solder leads to intermittent connections, and excessive heat damages sensitive ICs.

The chip mounting process follows a structured workflow, starting with solder paste application. A stencil (thin metal sheet with laser-cut apertures matching the chip’s pads) is placed over the PCB, and a squeegee deposits solder paste (a mixture of tin-lead or lead-free solder alloy and flux) onto the PCB’s pads. The paste’s viscosity and particle size are tailored to the chip package—fine-pitch BGAs (0.5mm pitch) require smaller solder particles (20–38μm) to avoid bridging between pads. Next, automated placement uses pick-and-place machines with vision systems (high-resolution cameras) to identify the PCB’s fiducial marks and align chips with the solder paste. The machine’s precision (±0.01mm) is critical for fine-pitch packages: a QFP with 0.4mm pitch has pads just 0.2mm wide, leaving minimal room for error. The machine uses vacuum nozzles to pick chips from reels or trays, then places them gently onto the solder paste—applying controlled pressure to ensure good contact without damaging the chip’s pins.

After placement, reflow soldering melts the solder paste to form permanent joints. The PCB passes through a reflow oven with a temperature profile tailored to the solder alloy: lead-free solder (e.g., Sn96.5Ag3.0Cu0.5) requires a peak temperature of 240–250°C, while leaded solder (Sn63Pb37) peaks at 215–225°C. The profile includes four stages: preheat (to activate flux and evaporate solvents), soak (to stabilize temperature and prevent thermal shock), reflow (to melt solder), and cool (to solidify joints). Flux in the paste removes oxidation from pads and chip pins, ensuring strong solder adhesion. Post-reflow inspection uses automated optical inspection (AOI) systems to check for defects: missing chips, misalignment, solder bridges (short circuits between pads), or insufficient solder (cold joints). For BGAs or other hidden-joint packages, X-ray inspection detects internal defects like voids (air bubbles in solder balls) that could cause reliability issues.

Key considerations for chip mounting include package compatibility and thermal management. The PCB’s pad design must match the chip’s package (e.g., BGA pad layout, QFP pin count) to ensure proper alignment. Heat-sensitive chips (e.g., microcontrollers with temperature limits of 125°C) require modified reflow profiles to reduce peak temperature exposure. For high-power chips (e.g., IGBTs in solar inverters), thermal vias or heat sinks are added to the PCB to dissipate heat during mounting and operation. In high-volume production, mounting machines are calibrated regularly to maintain precision—even a 0.02mm misalignment can render a fine-pitch chip unusable. For example, mounting a BGA-based 主控芯片 (MCU) on a wireless module PCBA requires strict control of solder paste volume (to avoid bridging) and reflow temperature (to prevent BGA ball cracking). Chip mounting is a make-or-break step in PCBA production; its precision and consistency directly determine the PCBA’s functionality and lifespan.