PCB News - PCB engineer test questions related test questions

one. Fill in the blanks

1. The interconnection lines on the PCB board can be divided into microstrip lines and strip lines according to their types.

2 The two factors that cause crosstalk are capacitive coupling and inductive coupling

3. Three elements of EMI: emission source, conduction path, sensitive receiving end

The thickness of 4.1OZ copper is 1.4 MIL

5. The speed of the signal in the PCB (Er is 4) stripline is: 6inch/ns

6. PCB surface treatment methods are: spray tin, immersion silver, immersion gold, etc.

7. The signal propagates along the 50 ohm impedance line. It encounters an impedance mutation point. The impedance here is 75 ohm. The signal reflex coefficient here is _(0.2)

8. According to IPC standard. PTH aperture tolerance: +/-3mil NPTH aperture tolerance: +/-2mil

9.1mm wide interconnection line (1OZ copper thickness) can carry 1 A current

10. The basic principle of differential signal line wiring: equal distance and equal length

11. In high-frequency PCB design, signal traces become part of the circuit. At frequencies higher than 500MHz, traces have characteristics of resistance, capacitance, and inductance.

12. The highest EMI frequency is also called the EMI emission bandwidth, and it is a function of the signal rise time rather than the signal frequency. (Note: The formula for calculating EMI emission bandwidth is f=0.35/tr

Where f-frequency (GHZ); tr-signal rise time or fall time (10% to 90% of the rise or fall interval time) ns).

13. The length of most antennas is equal to λ/4 or λ/2 of a specific frequency (λ is the wavelength). Therefore, in the EMC specification, wires or traces are not allowed to work below λ/20 of a certain frequency, because this will suddenly turn it into a high-performance antenna, and inductance and capacitance will cause resonance.

14. Ferrite beads can be seen as an inductor and a resistor in parallel. At low frequencies, the resistor is short-circuited by the inductor, and current flows to the inductor; at high frequencies, the high inductance of the inductor forces the current to flow to the resistor. At high frequencies, ferrite beads are used instead of inductors.

15. The best rule of layout is to minimize the magnetic flux.

Two. Judgment

1. The interconnection line on the PCB is the transmission line. (X)

2. The greater the dielectric constant of the PCB, the greater the impedance. (X)

3. Reducing the thickness of the bottom PP medium can reduce crosstalk. (X)

4. The impedance will change when the signal line crosses the plane. (Y)

5. The differential signal does not need to refer to the loop plane. (X)

6. Reflow soldering is applied to plug-in parts. Wave soldering is applied to patch parts. (X)

7. The loop of the high-frequency signal is to return along the shortest path between the source and the terminal. (X)

8. The impedance of the USB2.0 differential is 100 ohms. (X. I think it is 90)

9. The meaning of TG in PCB board parameters is the decomposition temperature. (X.Tg is high heat resistance.)

10 The signal current will concentrate on the surface of the wire at high frequencies. (Y)

Three choices

1 The factors that affect impedance are (A D)

A. Line width

B. Cable length

C. Dielectric constant

D. PP thickness

E. Green oil

2 Methods to reduce crosstalk (BCDE)

A. Increase the thickness of PP

B.3W principle (Note: The spacing between traces is twice the width of traces)

C. Maintain circuit integrity;

D. Orthogonal routing of adjacent layers

E. Reduce the length of parallel traces

3. What are the basic parameters of PCB board(A C D)

A. Dielectric constant

B. Loss factor

C. Thickness'

D. Heat resistance

E. Water absorption

4. EMI scan shows that the frequency exceeds the standard at 125MHZ. This phenomenon may be caused by which of the following frequencies (B.A is a bit like, but the multiplier is too far from B

A.12.5MHZ

B.25MHZ

C.32MHZ

D.64MHZ

5. Which of the following files are not needed when making PCB (B D)

A.silkcreen

B.pastmask

C.soldermask

D.assembly

6. According to IPC standard. Board warping should be <= (C)

A.0.5%

B.0.7%

C.0.8%

D. 1%

7. What factors will affect the price of PCB (A B C d)

A. Surface treatment method

B. Minimum line width and line spacing

8 C.VIA's aperture size and quantity

D. Number of layers

8. The following error occurs when navigating the netlist: ERROR: Canot find device file for'CN-MINPCI-126' The reason may be (A)

A. The package name is wrong

B. The package PIN corresponds to the schematic PIN incorrectly

C. The library is missing this packaged PAD

D. There is no such package in the parts library

Four. Term explanation

Microstrip: Refers to a PCB trace with a reference plane on only one side. The microstrip line provides the PCB with RF suppression, and can also tolerate clock or logic signals faster than the strip line. The disadvantage of the microstrip line is that the external signal layer of the PCB will radiate RF energy into the environment, unless there is a metal shield above and below this layer.

Stripline: Stripline refers to a transmission line with reference planes on both sides. Stripline can better prevent RF radiation, but it can only be used for lower transmission speeds, because the signal layer is between two reference planes, and there will be capacitive coupling between the two planes, which will reduce the edge rate of high-speed signals. . The capacitive coupling effect of the stripline is more significant when the edge change rate is faster than 1 ns.

55 Principle: When the clock frequency exceeds 5MHz, or the rise time is less than 5ns, a multilayer board must be used.

Skin effect: The skin effect refers to the deep flow of high-frequency currents on the surface of the conductor. Currents will not and cannot flow in large amounts in the center of traces, wires or planes. Most of these currents flow on the surface of the conductor. Different substances have different skin depth values.

Zero ohm resistance: The resistance value of a zero ohm resistor is not really 0 ohms, the typical value is about 0.05 ohms. A zero-ohm resistance is actually a small inductance (a zero-ohm inductance), so it can provide a small amount of series filtering.

Calculation of the trace length: microstrip line-Lmax = 9 * tr. (Lmax-the maximum length of the trace cm, tr-the rise time of the signal ns). Strip line-Lmax=7*tr. If the actual trace is longer than the calculated maximum trace length Lmax, then a terminal design is required to prevent reflection.