Optimizing Press Thermal Profiles for High Density Interconnect Coreless Assemblies
Optimizing coreless HDI thermal profiles requires synchronized heating ramps, controlled viscosity dwell windows, and low-rate cooling to prevent warp.
Thermal Ramp Control
Heating Rate
Regulation of the speed at which the temperature changes inside a furnace prevents damage to sensitive electronic assemblies. Precise thermal ramp control is necessary to manage the expansion of different materials at rates that do not cause mechanical failure. If the heat rises too quickly, the differential expansion between the resin and the copper can tear the plating inside the holes.
Thermal Gradient
Maintaining a steady increase in temperature allows the flux in the solder paste to activate and clean the surfaces before the solder melts. With thermal ramp control, the oven keeps the heating rate within the limits specified by the component manufacturers. This prevents the rapid outgassing of moisture that leads to the popcorning of plastic packages.
Component Protection
Sophisticated software algorithms monitor the output of the heating elements to stay within a narrow window of the target profile. The use of thermal ramp control minimizes the temperature difference between the small components and the large heat sinks on the same board. When the ramp is too steep, the heat does not have time to conduct through the substrate, leading to cold solder joints or warped boards.
This oversight is particularly critical during the transition from the soak zone to the reflow zone where the highest temperatures are reached. By smoothing these transitions, the process ensures that every joint reaches the liquidus state at nearly the same time, which reduces the occurrence of tombstoning or other placement defects.