Derating Nominal Equipment Speeds for Mixed Package Electronics Assembly Line Balancing
Derating nominal placement speeds based on package mass, feeder width, and vision complexity is required to establish accurate line balance and cost models.
Placement Downforce Displacement
Board Flexing
Mechanical deflection of the circuit board under the impact of the pick-and-place head alters the accuracy of component mounting. This placement downforce displacement occurs when thin boards bend under the force of the nozzle, causing the board to rebound as the nozzle lifts. Bending forces can shift adjacent parts that are already resting in wet paste.
Measuring and limiting this deflection is critical for high-density assemblies.
Paste Squeeze
Compressive forces applied to the solder paste during component placement alter the final solder joint shape. When placement downforce displacement is high, the head compresses the paste deposit, causing it to squeeze out beyond the copper pad boundaries. This squeezed paste can lead to solder bridging and short circuits during reflow.
Maintaining consistent placement force prevents these assembly defects.
Support Strategy
Firm support under the circuit board during assembly minimizes mechanical bending and ensures a stable surface for component placement. If placement downforce displacement is not controlled, the board acts like a spring and rejects the component as the nozzle retracts. Using dedicated support pins or vacuum plates under the board prevents the substrate from flexing.
These tooling supports are positioned away from double-sided components on the bottom layer. Keeping the board rigid ensures that small chip capacitors and resistors are mounted at the correct depth, raising the first-pass yield of the assembly line.