In addition to the use of a patch element, the newly designed circuit board removes special needs, it is a preferred patch component. The patch components are small, easy to weld, easy to maintain, decreased with cost, has become the default option for many device selection scenarios. Especially for resistance, capacitance, inductance, components used in these batch, are preferred when designing the preferred patch elements. This is because of the following reasons.
Compared with the in-line element, the patch element is small, light weight, easy to save and transport.
The volume and weight of the patch element has only about 1/10 of the traditional insert element. After the SMT is generally used, the volume of electronics is reduced by 40% to 60%, and the weight is reduced by 60% to 80%. High reliability, strong anti-vibration power, low solder joint defects, high frequency characteristics, reduce electromagnetic and radio frequency interference, easy to achieve automation, improve production efficiency, reduce cost reached 30% ~ 50%, save materials, energy, equipment , Human, working hours. If a commonly used patch resistance 0805 package or 0603 package is much smaller than we used before us. Dozens of straightforward resistors can be filled with a bag, but if they change to a patch resistor, they are enough to install thousands of or even 10,000. Generally preferred table stickers if the power can be satisfied.
The patch component is easily welded and disassembled than the straight interpolation element.
The patch element does not have to pass through the hole, with a small. The most troublesome of the insertion element is to disassemble, when disassembling on two or more layers of PCB boards, even if only two pins are, it is not easy, and it is easy to damage the board, and the piercence is Never use it. The removal of the patch element is much easier, and it is not easy to damage the circuit board. The main tools for disassembling the direct interposer are the absorber, the automatic absorber price is expensive, and it is not easy to maintain, it is easy to damage, or a pore blockage. The chip device is placed on the PCB pad during the welding process, and the interpolation device is generally dependent on manual discharge. Therefore, when mass production, the productivity of the patch devices will be much higher than the insert device. The insertion device often requires additional "clipping feet" after welding, which will affect the production efficiency when the production is very large.
The patch component is better than the high frequency characteristics of the straight interpolation element.
This is because the patch element is small and does not require aperture, thereby reducing stray electric fields and stray magnetic fields, which is very important in high frequency analog circuits and high-speed digital circuits. As shown in Figure 8.1, we can see the parasitic parameters of the resistor, mainly in parallel with stray capacitance CP, and the parasitic inductance LP and parallel capacitance caused by leads.
High frequency equivalent model of resistance
As shown in the figure, the straight-in-in-in-force is in the form of a "metal wire", the longer the wire, the greater the parasitic inductance. The pin length of the direct-inserted resistance is not too short, the reasons are three: first, straight insert resistance volume is relatively large, the shortest pin is also larger than the radius size of the resistance cross-sectional area; second, the pin of the straightforward resistance needs Through the PCB; third, when we bend the electric resistance tube foot, you need to leave a distance to avoid resistance, resulting in resistance damage. As shown in Figure 8.3, in contrast, the pins of the table stickers are very short, so the parasitic inductance of the table stickers resistance is very small.
Straight discharge resistance feet factory
Table sticker feet factory
The impedance of the ideal resistance should be independent of frequency, as shown.
Ideal resistance impedance graph
In a circuit with resistance, inductance, and capacitance, the obstacles acting on the current in the circuit are called impedance. The impedance common z is represented by a plural, referred to as a resistor, an implancation of an impedance, wherein the obstacles that the capacitor to DC power is referred to as a capacitive, inductance, in the circuit, the impedance of alternating current The impedance effect caused by an alternating current in the circuit is generally referred to as reactance. The unit of impedance is ohm.
The impedance is the total reaction of the components or circuit on the cycle of AC signals. AC AC test signal (amplitude and frequency). Impedance is a plural, including real and imaginary. The ideal resistance is the real part of the impedance, parasitic inductance and parasitic capacitance are impedance of impedance.
Simply put, we can first omit the parasitic parallel capacitance, which is an ideal inductor. When a parasitic inductor is connected in series, it is equivalent to an impedance to increase an imaginary portion. According to the inductive characteristics of the inductance, it is a straight flow, and the flow is blocked, it is equivalent to the high frequency impedance rise.
Impedance is represented by z = R + JX in a right angle coordinate system. So in the polar coordinate system, the impedance can be represented by amplitude and phase angle. The real and imaginary parts in the right angle coordinate system can be amplitude and phase in the translation of the math conversion. We can know by impedance formula.
So the result of the Zeng mode is the size of the impedance of a frequency point. As shown in Figure 8.5, we represent an impedance in the complex impedance plane.
Refact resistance plane indicates an impedance
When we discuss some circuits, we often need to know the impedance absolute value of each frequency point in each frequency point, such as signal integrity analysis, filter design, etc. of high-speed digital circuits. So we generally draw a function curve of an impedance and frequency, describe the impedance characteristics. We chose a 10 ohm resistor and set the parasitic capacitance of 0.2PF, a circuit with a parasitic inductance of 10NH or 20NH, and its impedance characteristics are shown in the figure.
Impedance characteristic curve of actual resistance
The patch component improves the stability and reliability of the circuit.
The seismic capacity deviation of the direct insert device, in some high reliability scenarios, need to reinforce the glue on the pipe footpoint of the insert device, as shown.
Vertical straightforward resistance point glue reinforcement process
Directive capacitive point glue reinforcement process
The table sticker is small due to small size, light weight, the same parameters, the vibration is small, and the shock has a small response to the pin. The pin of the table sticker is not a wire form of a direct insert, but a large-area metal surface is welded to a PCB pad. Therefore, the pin of the table sticker is rigid, and the earthquake resistance is stronger.
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