Lead-free solder paste is an environmentally friendly material that does not contain lead and plays a very important role in soldering work. And lead-free solder paste is one of the most important factors in obtaining high-quality solder joints in printed circuit board (PCB) assembly using surface mount components. A temperature profile is a function of temperature applied to a circuit assembly as a function of time, and when plotted on a Cartesian plane, at any given time during the reflow process, a curve is formed representing the temperature at a particular point on the PCB.
Several parameters affect the shape of the curve, the most critical of which are the conveyor speed and the temperature settings for each zone. Belt speed determines the duration that the board is exposed to the temperature set for each zone, increasing the duration allows more time to bring the circuit assembly closer to the zone's temperature setting. The sum of the durations spent in each zone determines the total processing time.
The high temperature of the lead-free solder paste produces a large temperature difference between the temperature of the PCB and the zone. Therefore, a graph must be made to determine the temperature profile of the PCB. Next is the outline of this step to generate and optimize the graph.
Before starting the profiling step, the following equipment and auxiliary tools are required: a temperature profiler, a thermocouple, a tool for attaching the thermocouple to the PCB, and a solder paste parameter sheet. A temperature profiling accessory kit, available from most major electronic tool suppliers, makes profiling convenient because it contains all the accessories needed (except for the curve meter itself).
But tin bars made of different alloy compositions also have different functions and uses. In addition to knowing this, welding technicians also need to pay attention to the following aspects:
One: The melting point of lead-free tin bars is very important, and several commonly used melting points should be paid attention to. The melting point is related to the alloy composition of the tin bar. The melting point of the tin bar of the tin-copper alloy is 227 degrees, and the temperature of the soldering work is between 270 and 300 degrees.
Two: Lead-free tin bars are usually used together with flux. It is necessary to choose a flux with good activity, high temperature resistance and no-cleaning, which can improve the welding power in the welding work.
Three: Use environmentally friendly lead-free soldering furnaces. When using lead-free tin wire, whether it is a solder furnace or solder flux, it is necessary to choose lead-free, so that it can meet the needs of environmental protection, rather than use it with a lead furnace.
Four: Pay attention to the height of the liquid level in the soldering furnace, and neither too much nor too little tin inside.
Five: There are many varieties of lead-free tin bars. It is necessary to find out which alloy composition of lead-free tin bars you choose, such as: tin-copper alloy Sn99.3Cu0.7 or silver-containing 0.3 lead-free tin bars Sn99.0Ag0. 3Cu0.7 or silver 3.0 lead-free tin bar Sn96.5Ag3.0Cu0.5 or high temperature lead-free tin bar, etc. The performance and usefulness of different alloys will be different. It is necessary to advance the power and ensure the effect during the whole welding work. Special attention must be paid when using lead-free solder bars.
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