Several issues that need to be paid attention to in PCB welding

时间2018/10/29 18:41:44

1. Possible conditions Transformation rate of the landing low signal edge

Meet the design Try to choose slower devices as much as possible while standardizing, usually at the time of device selection. And to prevent the mixed use of different types of signals, because fast-changing signals have potential crosstalk risks for slow-changing signals.

  2. Adopt Blocking measures

package land It will lead to an increase in the amount of wiring, and the circuit board to provide a land for high-speed signals is an effective way to deal with the problem of crosstalk. but. Make the originally limited wiring area more congested. In addition, the distance between grounding points on the ground wire shield to reach the expected destination line is very important, generally less than twice the length of the signal change edge. At the same time, the ground wire will also increase the signal dispersion capacitance, which will increase the transmission line impedance and slow down the signal edge.

  3. Reasonable Set up layers and wiring
Reduce the length of the parallel signal, reasonably set the wiring layer and wiring spacing. Shortening the distance between the signal layer and the plane layer, increasing the distance between signal lines, and reducing the length of parallel signal lines (within the critical length) can effectively reduce crosstalk.

  4. Settings Different wiring layers
And set the plane layer reasonably, set up different wiring layers for the signals of different speeds. It is also a good way to deal with crosstalk.

  5. Impedance Match

can also Greatly reduce the amplitude of crosstalk. If the impedance of the near or far end of the transmission line matches the impedance of the transmission line.

circuit board During use, the pads often fall off, especially when the circuit board is repaired. When using an electric soldering iron, it is very easy to cause the pads to fall off. The PCB factory analyzes the reasons for the fall off of the pads in this article. Take corresponding countermeasures for the reasons.

Welding when soldering circuit boards Analysis of the reason why the disk is easy to fall off

1. Plate quality problems. Because the resin glue adhesion between the copper foil of the copper clad sheet and the epoxy resin is relatively poor, in that case, even the large area of the copper foil of the circuit board copper foil is slightly heated or under mechanical external force, It is very easy to separate from the epoxy resin and cause problems such as the peeling of the pad and the peeling of the copper foil.

2, circuit board storage The influence of conditions. Affected by the weather or stored in a damp place for a long time, the circuit board absorbs moisture too high. In order to achieve the ideal welding effect, it is necessary to compensate for the heat taken away due to the volatilization of moisture when welding the chip. The temperature and time should be extended. Such welding conditions are likely to cause delamination between the copper foil of the circuit board and the epoxy resin.

3, soldering iron problem. The adhesion of general circuit boards can meet the requirements of ordinary soldering, and there will be no pad falling off. However, electronic products are generally likely to be repaired. Repairs are usually repaired by soldering with an electric soldering iron. The local high temperature of the electric soldering iron is often When the temperature reaches 300-400 degrees, the local temperature of the pad is too high, and the resin glue under the copper foil of the pad falls off due to the high temperature, and the pad falls off. When the soldering iron is disassembled, it is easy to attach the physical force of the soldering iron tip to the pad, which is also the cause of the pad falling off.

For the pads are easy to fall off under the conditions of use, The circuit board factory takes the following aspects to increase the number of soldering resistance of the circuit board pads as much as possible to meet the needs of customers.

1: The copper clad laminate is made of the base material produced by the authentic and quality-guaranteed manufacturer. Generally, the glass fiber cloth material selection and the pressing process of the genuine copper clad laminate can ensure that the solder resistance of the manufactured circuit board meets the customer's requirements.

2: The circuit board is vacuum packed before leaving the factory, and desiccant is placed to keep the circuit board in a dry state. Create conditions to reduce false welding and improve weldability.

3: In view of the thermal impact of the soldering iron on the pad during rework, we try to increase the thickness of the copper foil of the pad through electroplating, so that when the soldering iron heats the pad, the thermal conductivity of the thick copper pad is significantly enhanced and effectively reduced The local high temperature of the pad, and at the same time, the fast heat conduction makes the pad easier to remove. To achieve the solder resistance of the pad.




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