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PCB Circuit Board Reliable Soldering

PCB circuit board soldering is an important component in the electronics industry. Proper solder design and good processing are key factors in achieving reliable soldering. How to understand the word reliability? Reliable means that the solder joint itself has all the properties required, ensuring unmistakable work throughout the use of PCB Circuit Board.

Although the physical and chemical principles of all PCB circuit board welding processes are the same, the soldering of electronic PCB circuits board has its own advantages, namely high reliability and miniaturization, which are consistent with the characteristics of electronic products. The quality of PCB circuit board soldering is affected by many factors. For example, metal surface layer, plating and thickness, processing technology, method, and surface state before welding, welding composition, welding method, welding temperature and time, gap of metal to be welded, etc.

Not only the oxide on the surface of the lead of the soldered component but also the intermetallic compound condition of the internal structure of the lead is an important factor affecting the solderability of the lead, and the surface oxide of the PCB circuit board is also the main factor affecting the solderability of PCB circuits board.

Factors affecting PCB line welding

The design of the PCB circuit board affects the quality of the weld. In the layout, the PCB size is too large, although the welding is easier to control, but the long line impedance of the printed circuit line increases, the anti-noise ability decreases, and the cost of PCB circuit board increases; when the temperature is too small, the heat dissipation decreases, the welding is difficult to control, and adjacent lines are prone to mutual interference, such as The electromagnetic interference of the PCB circuit board. So we have to optimize the design of the PCB circuit board:

(1) Shorten the wiring between high frequency components and reduce EMI interference.

(2) Components with a large weight (eg more than 20g) shall be fixed by brackets and then welded on PCB circuit board.

(3) The heating element should consider the heat dissipation problem, prevent the surface of the component from having a large ΔT defect and rework, and the heat sensitive component should be away from the heat source on PCB circuit board.

(4) The arrangement of the components on PCB circuit board is as parallel as possible, so that it is not only beautiful but also easy to weld, and easy to be mass-produced. The PCB circuit board is designed to be optimal for a 4:3 rectangle. Do not mutate the wire width to avoid discontinuity of the wiring. When the PCB circuit board is heated for a long time, the copper foil is prone to expansion and fall off. Therefore, large-area copper foil should be avoided when design PCB circuit board.

2.2 The solderability of the PCB circuit board hole affects the soldering quality. The solderability of the PCB circuit board hole is not good, and the solder joint defect will be generated, which will affect the parameters of the components in the PCB circuit board, resulting in unstable conduction of the multilayer PCB circuit board components and the inner layer. Causes the entire PCB circuit board to fail. The so-called solderability is the property of the metal surface being wetted by the molten solder, that is, the metal surface of the solder forms a relatively uniform continuous smooth attached film. The main factors affecting the solderability of PCB printed circuit boards are:

(1) The composition of the solder and the properties of the solder. Solder is an important part of the soldering chemical process. It consists of a chemical containing a flux. The commonly used low melting point eutectic metal is Sn-Pb or Sn-Pb-Ag. The impurity content should be controlled by a certain ratio to prevent the oxide generated by the impurities from being dissolved by the flux. The function of the flux is to help the solder wet the surface of the PCB circuit board being soldered by transferring heat and removing rust. White rosin and isopropanol solvents are generally used.

(2) The soldering temperature and the cleanliness of the PCB CIRCUIT BOARD surface also affect the solderability reliability. When the temperature is too high, the solder diffusion speed is increased. At this time, the activity is high, and the PCB circuit board and the solder melted surface are rapidly oxidized, causing soldering defects, and the surface of the PCB circuit board is contaminated, which also affects the solderability and causes defects. Including tin beads, solder balls, open circuit, poor gloss and so on.

2.3 Welding defects caused by warpage PCBs and components are warped during the soldering process, and defects such as solder joints and short circuits are generated due to stress deformation. Warpage is often caused by temperature imbalances in the upper and lower parts of the PCB circuit board. For large PCB circuit board, warping occurs due to the weight of the PCB circuit board itself. The ordinary PBGA device is about 0.5mm away from the PCB printed circuit board. If the device on the circuit board is large, the normal shape will be restored as the PCB circuit board cools down, and the solder joint will be under stress for a long time. If the device is raised by 0.1mm, Enough to lead to open welding.

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