![]() Insufficient preheating temperature or insufficient flux activity Ĥ. There are residues on the board or pins ģ. The line distribution is too dense, the pins are too close or irregular Ģ. The abnormal connection formed by the solder between different adjacent wires or components is the so-called bridging phenomenon.ġ. 三、Solder joints with tin bridges after reflow soldering Add a reducing agent to the gold immersion solution to obtain a semi-replacement and semi-reduced composite gold layer, but the cost will increase by 2.5 times. The black pad is generated before soldering, and over-baking will deteriorate the plating Ĥ. The baking board before welding will not greatly promote the welding quality. The thickness of the nickel layer is at least 4μm, which can make the nickel layer relatively flat the thickness of the gold layer should not exceed 0.xn-1m-99b, too much gold will only make the solder joints brittle ģ. When the service life of the nickel tank is long, the P content in it will increase, which will accelerate the oxidation rate of nickel Ģ. Reduce the life of the nickel tank, strictly control the production, and control the content of P at about 7%. Under the action of GalvanicEffect, the nickel layer will continue to deteriorate.ġ. The deposited gold layer is relatively loose among atoms, and the nickel layer under the gold layer has the opportunity to continue to oxidize. The actual nickel layer has been The phenomenon of deterioration Ģ. The oxidation rate of nickel during the immersion gold process of the nickel layer is greater than the deposition rate of gold, so the nickel oxide produced is covered by the gold layer before it is completely dissolved, resulting in a good surface gold layer morphology. The black disk is mainly composed of Ni oxide, and the P content of the black disk surface is much higher than that of the normal Ni surface, indicating that the black disk mainly occurs after the bath is used for a period of time.ġ. The black pad refers to the good shape of the ENIG plating on the surface of the pad, but the nickel layer under the gold layer has deteriorated to produce a brittle black substance as long as it is nickel oxide, which poses a great threat to the reliability of the solder joint. Adjust the original process parameters when soldering 025 components to slow down the preheating curve's creeping slope, and make adjustments in solder paste printing. The wetting behavior of various solders in a nitrogen-protected environment can be significantly improved Ħ. Set the process parameters reasonably, increase the preheating or welding temperature appropriately to ensure sufficient welding time ĥ. The brass pins should be plated with a layer of 1~3μm before welding, otherwise the Zn in the brass will affect the welding quality Ĥ. Generally speaking, a plating layer of at least 5μm thickness is required to ensure that the material does not expire within 12 months ģ. Select the plate with the coating quality up to the required quality. Store plates and components as required, and do not use deteriorated welding materials Ģ. After more and more 025 components are used, due to the small amount of solder paste printed, the flux in the solder paste quickly volatilizes under the original temperature curve, which affects the wettability of the solder paste ġ. In addition, the mismatch between the plating layer and the solder may also cause poor wetting Ħ. The preheating temperature is too low or the flux activity is not enough, so that the flux cannot effectively remove the oxide film on the pad and pin surface ĥ. Compared with SnPb, commonly used lead-free solder alloys have higher melting points and greatly reduced wettability, requiring higher soldering temperatures to ensure soldering quality Ĥ. Insufficient coating thickness or poor processing, it is easy to be damaged during the assembly process ģ. The plating layer on the surface of the pad or pin is oxidized, and the existence of the oxide layer prevents the contact between the solder and the plating layer Ģ. Generally, poor wetting means that the solder joint solder alloy is not spread out well, so that a good solder joint cannot be obtained and directly affects the reliability of the solder joint.ġ. ![]() 一、Non-wetting/poor wetting of reflow solder joints The most problematic process stage in the SMT process is reflow soldering. SMT reflow soldering refers to the use of solder paste to connect multiple SMT electronic components to the PCB board, and then the solder paste is melted by controlling the heating to achieve permanent bonding. Common defects and solutions after SMT reflow soldering
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