(1) the right to choose temperature range. Solder is temperature sensitive material. Sn based solder at low temperature, for example, allotropic changes easily, brittle, its rate of change in - 45 'C fastest, so not suitable for use in the low temperature; At high temperature, the creep characteristics significantly, in the 100 'C high temperature strength decreases greatly. Therefore when using Sn, Pb eutectic solder, should design the substrate temperature (including internal fever) limit under 90 'C as much as possible.
(2) the applicability of the mechanical properties. Sn, Pb solder tin solder, mechanical stress itself is not high, the welding areas prone to plastic deformation, and ultimately form a solder crack. Under any conditions of use, should be paid attention to when choosing a solder alloy must meet the requirements of mechanical strength.
(3) the weld metal and solder composition to form a variety of intermetallic compounds. These compounds have the properties of hard and brittle, will become a solder crack. Especially in the assembly of surface mount components, solder and weld metal interface stress is set in place, easy to form a double disadvantage. Due to the formation of the intermetallic compound is related to temperature and time, so the welding meet at low temperatures and in a short period of time as far as possible to complete.
(5) prevent corrosion phenomena. Under the condition of welding, weld metal will dissolve in the molten solder alloy, this phenomenon is called corrosion. In SMT soldering temperature range, the dissolution rate of Sn, Pb solder cicc fastest, the second is silver. In SMC/SMD, with silver electrodes, at this time in order to prevent the solder corrosion phenomenon, often in the components or lead electrode Ni plating layer, and then Sn plating. To prevent the corrosion is the best way to use add silver solder, therefore often added in the Sn, Pb (1% ~ 3%) Ag alloy solder.
(6) to prevent oxidation of solder and deposition. Dip soldering and wave soldering process, during the stop welding, solder static, the longer the scum of the liquid surface oxidation quantity. So, should add appropriate anti-oxidation additives in solder groove, in order to reduce the oxidation speed and improve the wettability. In addition, due to the proportion of various components in the different solder, so the condition of the component uneven solder groove. Especially in adding Ag solder, the Ag than major, easy to deposit in the bottom of the solder groove, so must be fully mixing in the welding process. In addition, can jam deposition Ag solder spray exports, must pay attention to during welding operations.
1, the PCB is what mean?
Usually completes the circuit without mount components of the circuit board is called the "PCB"
2, SMT is what mean?
SMT is the process to install components in circuit boards is called SMT.
3, PCBA, what meaning be?
Is through the PCB circuit board processing, SMT processing, DIP plug-in processing, assembly, testing, packing, etc. The whole production process, Advancing Tech co., LTD is a manufacturer specialized in PCBA. Company in baoan district solid defensibly, survived for more than ten years in the industry, is an influential brand.
PCB, for printed circuit board, which includes rigid, flexible, and just, flexible combination of single-sided, double-sided and multi-layer PCB, as shown in figure 1.
Pcb processing as the most important components, the basis of electronic products used as electronic interconnection and installation of the base plate, as shown in figure 2.
Different categories of PCB, its manufacturing technology also is not the same, but the basic principle and method were roughly the same, such as plating, etching, resistance welding process methods are used. In all kinds of PCB, multilayer PCB rigidity is the most widely used, its manufacturing method and technological process for the most representative, is also the foundation of other categories PCB manufacturing process.
Understand the PCB manufacturing methods and processes, to master the basic ability of PCB manufacturing process, is the basis of the PCB manufacturability design.
This section will simple introduce the traditional rigid multilayer PCB and high density interconnect PCB manufacturing method and process and basic process capability.
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