Preheat – During this phase the components, PCB and solder are all heated to a specified soak or dwell temperature being careful not to heat too quickly (usually no more than 2✬/second - check solder paste datasheet).
The main aim being to transfer enough heat into the assembly to melt the solder and form the solder joints without causing any damage to components or PCB. Within a typical reflow soldering profile there are usually four stages – Preheat, soak, reflow and cooling.
#BGA REFLOW FULL#
Ideally more thermocouples should be used to measure the full range of temperatures across the PCB – known as ‘Delta T’. It is recommended to have at least one thermocouple located on a pad towards the edge of the PCB and one thermocouple located on a pad towards the middle of the PCB. In order to create a reflow profile thermocouples are connected to a sample assembly (usually with high temperature solder) in a number of locations to measure the range of temperatures across the PCB. The calculation is for HEATED LENGTH – NOT OVERALL OVEN LENGTH. Note that the overall length of the oven will exceed 10 feet including the cooling section and conveyor loading sections. Oven heated length = 120 inches (10 feet) Therefore, the reflow oven must have a process speed of at least 30 inches per minute.ĭetermine oven chamber heated length with process speed equation: Load Factor = 0.8 (2-inch space between boards)Ĭalculate Line Speed: (3 boards/min) x (8 inches/board) How long an oven do I need to process boards at this throughput? The solder paste manufacturer recommends a 4 minute, three step profile. Process speed = Oven chamber heated lengthīelow is an example of calculation to establish the correct oven size:-Īn SMT assembler wants to produce 8-inch boards at a rate of 180 per hour. To be able to select the correct size reflow oven the process speed (defined below) must be greater than the minimum calculated line speed.
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