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★ evaluate lead-free solder suppliers
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(1) lead-free solder suppliers must have the self-testing capability PB content <1000PPM cadmium <20PPM
(2) technical service capabilities of the supplier of lead-free solder
(3) a difficult lead-free solder applications in its wettability than traditional solder SN-PB to be a lot worse, rely on the flux help.
Chapter IV lead-free soldering technology
The basic characteristics of lead-free welding technology
An available lead-free solder SN-CU SN-AG SN-AG-CU melting points are about 220 ℃, 40 ℃ or so higher than the traditional SN63-PB37, melting point 183 ℃, so the need for higher lead-free solder welding temperature, followed by equipment, electronic components and pcba china, heat resistance and higher requirements.
2, on the other hand, all lead-free solder wetting properties are weaker than the SN of PB, lead-free soldering is required to achieve and lead the same welding quality: First, require more precise control of welding processes, followed by the need to develop new shaped flux to compensate for the lack of wetting of lead-free solder defects, of course, whether or not to use the inert gas protection is also a need to assess the problem.
★ The above two points is a lead-free soldering the fundamental source of the many special requirements, then we will elaborate electronic pcb assembly welding technology, namely, hand-soldering iron, dip soldering, wave soldering and reflow in the specific application requirements.
Recommend the use of lead-free solder
For manual soldering solder, dip soldering and wave soldering applications, we recommend using the binary lead-free solder in SN-CU SN - 0.7CU eutectic solder.
The main reason of the following aspects:
1, due to the melting point difference between the various elements of the lead-free solder, so as far as possible use the most simple binary alloy. Elements more and more difficult it is to form a uniform microstructure;
2, soldering, solder alloy with the eutectic composition of the welding performance is the best;
The practicality of the SN-CU Solder has been widely confirmed. NEMI north art industry in 2000 also suggested that the recommended lead-free solder lead-free wave soldering using SN-0.7CU solder;
SN-CU is the lowest cost of all lead-free solder, solder processing-based Chinese electronics industry is very important. We calculated an electronics factory in the average monthly use 1 ton of solder, taking into account the prices and costs, as well as dross, clear furnace brought the loss, a year down the SN-CU solder lead-free solder than the series of SN AG / SN AG CU save the cost of 100 million yuan.
On lead-free reflow soldering is recommended SN AG / SN AG CU solder reflow peak temperature of not more than 250 ° C due to the limitations of electronic components thermal shock resistance,
SN AG / SN AG CU Lead-free solder melting point lower than SN-CU series melting point 6 ℃.