Selective Solder Process Windows for Plated through Hole Components
Selective solder process windows require matching top-side preheat above 110C with precise 3-second pin dwell times to achieve 75 percent Class 3 barrel fill.
Contact Dwell Time
Process Duration
The period during which a circuit board surface remains in direct contact with molten solder is a primary factor in selective or wave soldering. This interval, commonly known as contact dwell time, governs the amount of heat energy transferred to the board and the solder joint. If the duration is too brief, the solder will not fill the plated through-holes completely, while excessive exposure causes thermal damage to the substrate.
Thermal Transfer
Heat energy must flow from the solder wave into both the copper pads and the component leads to initiate wetting. A minimum period is required to bring these surfaces to the proper soldering temperature and promote intermetallic layer growth. Modern lead-free alloys demand slightly longer contact to overcome their slower wetting kinetics compared to traditional tin-lead options.
Thick multilayer boards or those with heavy copper planes act as thermal sinks, requiring a prolonged interface to achieve acceptable top-side fillet rise.
Control Parameter
Conveyor speed and nozzle height represent the primary machine adjustments used to govern this variable. Direct measurements are obtained using thermal profile boards equipped with sensors that register the contact duration. Process engineers monitor these values to maintain a window that prevents board blistering while ensuring sound joints.