![]() 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. We manufacture and sell a wide variety of soldering products including wire solder, bar solder, liquid flux, gel flux, and solder pastes.To be able to select the correct size reflow oven the process speed (defined below) must be greater than the minimum calculated line speed. Newer Type 4 solder pastes typically perform equal to or better than Type 3 solder pastes.įCT Assembly is ready to meet your needs for Type 3, 4 and 5 solder pastes. Most solder paste manufacturers correct these issues by adjusting the formulas for Type 4 and 5 solder pastes. This is due to a higher potential for oxidation of Type 4 and 5 solder powders. Type 4 and 5 solder pastes can generate more random solder balling and graping than Type 3 with certain solder paste formulations. The shelf life of Type 4 and 5 solder paste is typically shorter than Type 3 due to a higher rate of reaction between the flux and solder powder. This higher rate of reaction leads to potential issues when using Type 4 and 5 solder pastes. Therefore, smaller solder powders react more quickly than larger solder powders. The rate of chemical reaction with the solder powder is directly proportional to the surface area of the solder powder. For the same mass of solder powder, the surface area of Type 4 solder powder is roughly 20% higher than Type 3, and the surface area for Type 5 solder powder is roughly 75% higher than Type 3. The surface area of the smaller solder powder types is significantly higher than the larger solder powder types. Smaller solder powder sizes like Type 4 and Type 5 give improved printability but also can create some issues due to chemical reactions with the solder powder. This combination allows for printing of even the finest of components. The increase in transfer efficiency is dramatic when Type 4 or 5 solder pastes are used along with fine grain steel stencils coated with NanoSlic Gold. ![]() Fine grain laser cut steel stencils along with NanoSlic Gold coating give a substantial increase in transfer efficiency as compared to standard steel stencils. This is especially true when these solder pastes are coupled with stencil technologies designed to enhance printing. Type 4 or 5 solder pastes enhance printing for miniaturized components. At smaller area ratios this difference in transfer efficiency becomes less distinct. In general, Type 5 gives higher transfer efficiency than Type 4 solder paste, and Type 4 gives higher transfer efficiency than Type 3 solder paste. ![]()
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