1/7/2024 0 Comments Define reflowThe longer a system can cool down, the more Galden condensates and can be reused in the following soldering cycles.Ī powerful cooling system is key to reduce the waiting period between several soldering cycles. This also helps to reduce costs because Galden is quite expensive. It is important to remain the system closed, until the vapour condensates and the Galden is liquid again. When the temperature decreases there is still a lot of vapour in the process chamber. Typically, this happens around 180☌, that corresponds to 356☏. The solder paste will melt as soon as the PCB reaches the appropriate temperature, which depends on the solder paste that is used. This heats up the PCB, the components and the solder paste that is applied between them. While the Galden is condensing, it transfers the thermic energy evenly into the assembly. The vapour is displacing nearly all the oxygen, this prevents oxidation on the assembly. The medium condenses at the surface of the assembly. The circuit board is then exposed to this vapour. When the Galden is boiling, a vapour arises which is heavier than air. The soldering process starts by heating the system and following the predetermined temperature course. It is also important for the correct nozzle to be selected for the component type to be placed – a range of different component placement nozzles can be seen below:-Īfter the board has been prepared with solder paste and the components have been attached to the appropriate contacts, the board is placed in the vapour phase soldering machine. Quite often this centroid data is exported from the PCB design software but sometime is not available and so the service to generate the centroid file from Gerber data is offered by Surface Mount Process.Īll components placement machines will have a ‘Placement Accuracy’ specified such as:. This will lead to inconsistent results after reflow soldering process.Ĭomponent placement programs can be created using the pick and place machines but this process isn't as accurate as taking the centroid information directly from the PCB Gerber data. If component packages are not taught in the correct way it can cause the machines vision system to not see each part in the same way and so variation in placement will be observed. The placement of surface mount components must be repeatable and so a reliable, well maintained pick and place machine is necessary. Heating too quickly can cause defects such as components to crack and the solder paste to splatter causing solder balls during reflow. 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. 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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