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Contact: Ms Mary Huang
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Easy Implementation Of Lead-free Solder Repair In PCB Assembly

               PCB assembly due to wettability and lack of core suction, to achieve lead-free welding is difficult to rework, is it possible to achieve a variety of different components of lead-free welding is impossible? In this paper, we will introduce a method that can easily realize the rework of lead-free solder.PCB Assembly

               Rework is an important part of the production process of lead-free PCB assembly, especially during the initial transition period when each link in the supply chain forms an information curve. However, due to the need for warranty, there is still a problem of rework throughout the life cycle of the product.PCB Assembly

                It has been found that lead-free solder alloys are usually not as easy to moisten and Wick as SN/PB solder, so rework of lead-free solder is difficult, and its application in QFP is an obvious example. Despite these differences, successful rework methods (i.e., manual and semi-automatic) have been developed for lead-free solders (SN/AG/CU or SN/AG) for different components, such as discrete components, surface array encapsulation, and so on, using flux gels, pen fluxes, and wicking solders. Most rework equipment for SN/PB can still be used in lead-free solder. Welding parameters must be adjusted to apply to higher melting temperatures and lower wettability of lead-free solders. Other preventative methods used in SN/PB rework, such as the board drying when necessary, still apply to the rework of lead-free solder. Studies have shown that reliable lead-free solder joints with suitable particle structures and formed intermetallic compounds can be produced using appropriate rework processes.

               Special attention should be paid to the possibility of reducing the negative impact of rework on solder joints, components and PCB. Because of the rising of welding temperature, the z-axis thermal expansion coefficient (CTE) mismatch between laminated material, glass fiber and Cu, and the more stress exerted on the CU layer, it is possible that the cracking of CU in the plating-through hole can occur, which leads to the failure. This is a rather complex problem, because it is determined by many variables, elephant PCB layer and thickness, laminating material, rework temperature curve, cu layout and guide hole geometry (such as aperture ratio). To determine the conditions under which the lower pressure material (such as high TG, low CTE) can replace the traditional FR4, to meet the requirements of lead-free welding, there is much work to be done. This is not to say that lower-cost materials (such as CEM, FR2, etc.) cannot be used in lead-free soldering. In fact, these methods have been applied in mass production and the application is checked on the basis of each application. The effect of rework on pads and mask adhesion must be carefully assessed.PCB Assembly

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