PCBA Tech - SMT placement classification and selection of chip inductors

1. Classification of SMT surface mount methods

1. According to the different processes of SMT, SMT is divided into dispensing process (wave soldering) and solder paste process (reflow soldering). Their main differences are:

l The process before patching is different, the former uses patch glue, and the latter uses solder glue.

l The process after patching is different. The former passes through the reflow oven only for fixing, but also has to pass through wave soldering, and the latter passes through the reflow oven for soldering.

2. According to the process of SMT, it can be divided into the following types

A type of assembly that only uses surface mount components

IA has only surface mount single-sided assembly

Process: screen printing solder paste => mounting components => reflow soldering

IB has only surface mount double-sided assembly

Process: screen printing solder paste => mounting components => reflow soldering => reverse side => screen printing solder paste => mounting components => reflow soldering

Type 2: Assembly with surface mount components on one side and a mixture of surface mount components and perforated components on the other side

Process: Silk screen solder paste (top side) => mounting component => reflow soldering => reverse side => dispensing (bottom side) => mounting component => drying glue => reverse side => inserting component => wave soldering

The third category: assembly with perforated components on the top surface and surface mount components on the bottom surface

Process: Dispensing => Mounting Components => Drying Glue => Backside => Inserting Components => Wave Soldering

2. Selection of chip inductors and component performance testing in SMT chip processing

SMD inductor selection:

1. The net width of the SMD inductor should be smaller than the net width of the inductor to prevent excessive solder from causing excessive tensile stress to change the inductance value during cooling.

2. The precision of chip inductors available on the market is mostly ±10%. If you want the precision to be higher than ±5%, you need to order in advance.

3. Many chip inductors can be soldered by reflow soldering and wave soldering, but some chip inductors cannot be soldered by wave soldering.

4. When repairing, it is not possible to exchange patch inductors only by inductance. It is also necessary to know the task frequency band of the chip inductor to ensure the task function.

5. The shape and size of the chip inductors are basically similar, and there is no clear mark on the shape. When hand soldering or hand patching, don’t get the wrong position or take the wrong parts.

6. There are currently three rare chip inductors: 1. High-frequency inductors for microwaves. Suitable for use in frequency bands above 1GHz. 2. High-frequency chip inductors. It is suitable for resonant circuit and frequency selective circuit. 3. Universal inductance. Generally applicable to circuits of tens of megahertz.

7. Different products have different coil diameters and opposite inductances, and the DC resistances appearing are also different. In the high-frequency circuit, the DC resistance has a great influence on the Q value, so you should pay attention to it when designing.

8. It is also a goal of chip inductors to allow large currents to pass. When the circuit needs to bear large currents, it is necessary to think about this goal of the capacitor.

9. When a power inductor is used in a DC/DC converter, its inductance indirectly affects the task form of the circuit. In theory, the method of increasing or decreasing the coil can often be used to change the inductance to achieve good results.

10. Wire-wound inductors are commonly used in communication equipment operating in the 150~900MHz frequency band. In circuits with frequencies above 1GHz, microwave high-frequency inductors must be selected.

The above are the top ten considerations when selecting chip inductors in SMT chip processing. Better use of chip inductors can better ensure the quality of SMT chip processing.