Temperature curve setting preparation
The correct temperature profile will ensure high-quality solder joints. In the PCB assembly using surface mount components, an optimized reflow temperature profile is one of the most important factors to obtain high-quality solder joints. The temperature curve is a function of the temperature applied to the circuit assembly versus time. When drawing on the Cartesian plane, at any given time during the reflow process, the temperature at a specific point on the PCB forms a curve.
Several parameters affect the shape of the curve, the most important of which is the speed of the conveyor belt and the temperature setting of each zone.
The belt speed determines the duration of exposure of the board to the temperature set in each zone. Increasing the duration can allow more time for the circuit assembly to be closer to the temperature setting of the zone. The sum of the duration spent in each zone determines the total processing time.
The temperature setting of each zone affects the temperature rise speed of the PCB, and high temperature produces a larger temperature difference between the temperature of the PCB and the zone. Increasing the set temperature of the zone allows the board to reach a given temperature faster. Therefore, a graph must be made to determine the temperature curve of the PCB. Next is the outline of this step to generate and optimize graphics.
Before starting the curve step, the following equipment and auxiliary tools are needed: temperature curve meter, thermocouple, tool for attaching thermocouple to PCB, and solder paste parameter table. The temperature curve accessory kit can be purchased from most major electronic tool suppliers. This kit makes it easy to create curves because it contains all the necessary accessories (except for the curve meter itself).
COB bonding processing 3
Many reflow soldering machines now include an on-board thermometer and even some smaller, inexpensive countertop furnaces. Thermometers are generally divided into two categories: real-time thermometers, which instantly transmit temperature data and make graphs; and another type of thermometers sample and store data, and then upload them to the computer.
The thermocouple must be long enough and able to withstand the typical furnace temperature. Generally, a thermocouple with a smaller diameter has a small thermal mass and a fast response, resulting in accurate results.
There are several ways to attach the thermocouple to the PCB. The better way is to use high temperature solder such as silver/tin alloy with the smallest possible solder joints. Another acceptable method, fast, easy, and accurate enough for most applications, is to cover the thermocouple with a small amount of thermal compound (also called thermal grease or thermal grease) spots, and then use high-temperature tape (such as Kapton) to stick it. live. Another way to attach thermoelectric logs and pin couples is to use high-temperature adhesives, such as acrylate adhesives. This method is usually not as reliable as other methods. The attachment position should also be selected. It is usually best to attach the thermocouple tip between the PCB pad and the corresponding component pin thermocouple attachment position diagram or metal end. The solder paste characteristic parameter table is also necessary, and the information it contains is essential to the temperature profile, such as the desired duration of the temperature profile, solder paste activation temperature, alloy melting point and the desired maximum reflow temperature.
