PCB engineer interview questions, see if you know all of them?

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PCB engineer interview questions, see if you know all of them? [Copy link]

The following are interview questions for PCB engineers at a company in Shenzhen. Let’s see how many of them you can answer. (The answer is at the bottom)

1.The interconnections on PCB can be divided into () and () by type.

2.The two factors that cause crosstalk are () and ().

3. The three elements of EMI: ().

The thickness of 4.1OZ copper is ().

5. The speed of the signal in the strip line of PCB (Er is 4) is: ().

6. The surface treatment methods of PCB are: (). 7. A signal propagates along a 50-ohm impedance line and encounters an impedance mutation point where the impedance is 75 ohms. The signal reflection coefficient at this point is (). 8. According to the IPC standard, the PTH aperture tolerance is: (), and the NPTH aperture tolerance is: ().

A 9.1mm wide interconnect (1OZ copper thickness) can carry () current.

10. Basic principles of differential signal line wiring: ().

11.In high-frequency PCB design, signal traces become part of the circuit. When the frequency is higher than 500MHz, the traces have () characteristics.

12.The highest EMI frequency is also called (), which is a function of the signal rise time rather than the signal frequency. 13. The length of most antennas is equal to λ/4 or λ/2 (λ is the wavelength) of a certain frequency. 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-efficiency antenna, which will cause resonance. 14. Ferrite beads can be regarded as (). At low frequencies, the resistor is short-circuited by the inductor and the current flows to (); at high frequencies, the high inductive reactance of the inductor forces the current to flow to (). At high frequencies, ferrite beads are used instead of inductors.

15. The best principle for layout and routing is ().

[color= rgb(51, 51, 51)] 2. Judgment

[/color ]

1. The interconnection lines on PCB are transmission lines ( )

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

3. Reducing the thickness of the PP dielectric can reduce crosstalk ( )

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

5. The differential signal does not require a reference loop plane ( )

6.Reflow soldering is applied to plug-in parts, and wave soldering is applied to patch parts ( )

7. The loop of high-frequency signal returns along the shortest path between the source and the terminal ( )

8.The differential impedance of USB2.0 is 100 ohms ()

9.The meaning of TG in PCB board parameters is decomposition temperature ()

10. Signal current will be concentrated on the surface of the wire at high frequency ( )

3. Choose

1. The factors that affect impedance are ( )

A. Line width

B. Line length

C.Dielectric constant

D.PP thickness

E.Green oil

2. Methods to reduce crosstalk ( )

A. Increase PP thickness

B. 3W principle

C. Maintain loop integrity

D. Adjacent layer routing is orthogonal

E.Reduce the length of parallel traces

3. What are the basic parameters of PCB board materials ( )

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 ( )

A.12.5MHZ

B.25MHZ

C.32MHZ

D.64MHZ

5. Which of the following files are not required when making PCB ( )

A.silkcreen

[ color=rgb(51, 51, 51)]B.pastmask

C.solder mask

D.assembly

[align= left]6. According to IPC standards, the warp should be <= ( )

[size= 17px]A.0.5%

B.0.7%

C.0.8%

[size=17px ]D.1%

[ size=17px]

[size =17px]7. What factors will affect the price of PCB ( )

[font =Optima-Regular, PingFangTC-light]A. Surface treatment

B.Minimum line width and line spacing

Aperture size and number of C.VIA

[color =rgb(51, 51, 51)]D. Number of board layers

[align= left]

8. The following error occurs when exporting the netlist: ERROR: Canot find device file for'CN-MINPCI-126' The reason may be ( )[/size ]

A. Package name Wrong

B. The package PIN and the schematic PIN correspond incorrectly

C. The PAD of this package is missing in the library

[ color=rgb(51, 51, 51)]D. This package is not available in the parts library[/align ]

4. Explanation of terms

[color=rgb(51) , 51, 51)]

Microstrip line (Microstrip):

[ color=rgb(51, 51, 51)]Stripline:

55 principle:

Skin effect:

[color=rgb (51, 51, 51)]Zero ohm resistor:

[ color=rgb(51, 51, 51)]Calculation of trace length:

[ align=left]

Answer:

1. Fill in the blanks

1 .The interconnection lines on PCB can be divided into microstrip lines and strip lines according to their types. 51)]

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

/size]

3. The three elements of EMI: emission source, conduction path, and sensitive receiving end.

[ /size]

The thickness of 4.1OZ copper is 1.4 MIL/35um.

/size]

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

/size]

6. PCB surface treatment methods include: tin spraying, immersion silver, immersion gold, etc.

/size]

7. The signal propagates along a 50-ohm impedance line and encounters an impedance mutation point where the impedance is 75 ohms. The signal reflection coefficient at this point is (0.2).

/size]

8. According to IPC standards, the PTH aperture tolerance is: +/-3mil, and the NPTH aperture tolerance is: +/-2mil.

/size]

9.1mm Wide interconnects (1OZ copper thickness) can carry 1A of current.

[ /size]

10.The basic principle of differential signal line routing: equidistant and equal length.

11. In high-frequency PCB design, signal traces become part of the circuit. At frequencies above 500MHz, the traces have resistance, capacitance, and inductance characteristics. 12. The highest EMI frequency is also called the EMI emission bandwidth, which 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 (the time between 10% and 90% of the rise or fall interval, ns).

13. The length of most antennas is equal to λ/4 or λ/2 (λ is the wavelength) of a certain frequency. 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-efficiency antenna, and the inductance and capacitance will cause resonance.

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

15. The best principle for layout and wiring is to minimize magnetic flux.

2. 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)

[font=Optima-Regular, 3. Reducing the thickness of the PP dielectric can reduce crosstalk (X)

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

5. Differential signals do not require a reference loop plane (X)

6. Reflow soldering is applied to plug-in parts, and wave soldering is applied to SMD parts (X)

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

8. The differential impedance of USB2.0 is 100 ohms (X)

9. TG in PCB board parameters means decomposition temperature (X, Tg is high heat resistance)

10. Signal current will be concentrated on the surface of the wire at high frequency (Y)

51)]

3. Select

1. Factors affecting impedance are (AD)

A. Line width

B. Line length

C.Dielectric constant

D.PP thickness

E.Green oil

2. Methods to reduce crosstalk (BCDE)

A. Increase PP thickness

B.3W principle (Note: the trace spacing is twice the trace width)

C. Maintain loop integrity

D. Adjacent layer routing is orthogonal

E. Reduce the length of parallel routing

3. What are the basic parameters of PCB board materials (ACD)

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. 12.5MHZ

B. 25MHZ

C.32MHZ

D.64MHZ

5. Which of the following files are not required when making PCB (BD)

A.silkcreen

B.pastmask

C.soldermask

D.assembly

6. According to IPC standards, the board warp should be <= (C)

A.0.5%

[color=rgb (51, 51, 51)]B.0.7%

[ color=rgb(51, 51, 51)]C.0.8%

[align= left]D.1%

7. What factors will affect the price of PCB (ABCD)

[ align=left]A. Surface treatment[ /align]

B. Minimum line width and line spacing

[ font=Optima-Regular, PingFangTC-light]C.VIA aperture size and number

D. Number of board layers

[color =rgb(51, 51, 51)]

[color= rgb(51, 51, 51)]8. The following error occurs when importing the network table: ERROR: Cannot find device file for'CN-MINPCI-126' The reason may be (A)[/color ]

A. The package name is wrong[/ B. Package PIN and schematic diagram PIN correspondence is incorrect

C. The PAD for this package is missing in the library

[color=rgb(51, 51, 51) ]D. This package is not available in the parts library

[color=rgb (51, 51, 51)]IV. Terminology Explanation

[ color=rgb(51, 51, 51)]

[color =rgb(51, 51, 51)]Microstrip:

[color= rgb(51, 51, 51)]Microstrip line refers to a PCB trace with a reference plane on only one side. Microstrip line provides PCB with RF The disadvantage of microstrip is that the signal layer outside the PCB will radiate RF energy into the environment unless there is a metal shield above and below this layer.

[ /size]

Ribbon Stripline:

[font=Optima-Regular,[PingFangTC-light] Stripline refers to a transmission line with reference planes on both sides. Stripline can effectively 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, resulting in a lower edge change rate of high-speed signals. The capacitive coupling effect of stripline is more significant when the edge change rate is faster than 1ns. Principle 55: When the clock frequency exceeds 5MHz, or the rise time is less than 5ns, a multilayer board must be used. Skin effect: Skin effect refers to the high-frequency current flowing in the skin depth of the conductor surface. Current will not and cannot flow in large quantities in the center of the trace, wire or plane. Most of these currents flow on the surface of the conductor. Different materials have different skin depth values.

Zero ohm resistor:

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

Calculation of trace length:

Microstrip line - Lmax=9×tr. (Lmax-maximum length of trace cm, tr-signal rise time ns). Stripline - 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.

PingFangTC-light]The resistance of a zero-ohm resistor is not really 0 ohms, and the typical value is about 0.05 ohms. A zero-ohm resistor is actually a small inductor (a zero-ohm inductor), so it can provide a small amount of series filtering effect.

Calculation of trace length:

Microstrip line - Lmax=9×tr. (Lmax-maximum length of the trace cm, tr-rise time of the signal ns). Stripline - Lmax = 7 × tr. If the actual routing is longer than the calculated maximum routing length Lmax, a terminal design is required to prevent reflections.PingFangTC-light]The resistance of a zero-ohm resistor is not really 0 ohms, and the typical value is about 0.05 ohms. A zero-ohm resistor is actually a small inductor (a zero-ohm inductor), so it can provide a small amount of series filtering effect.

Calculation of trace length:

Microstrip line - Lmax=9×tr. (Lmax-maximum length of the trace cm, tr-rise time of the signal ns). Stripline - Lmax = 7 × tr. If the actual routing is longer than the calculated maximum routing length Lmax, a terminal design is required to prevent reflections.

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This question is too difficult.

常见泽1

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Many people don't! ! !

shakencity

Every word seems familiar, every sentence seems familiar, it seems there are blind spots everywhere, I need to learn more, I can't stop,

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