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PCB Inspection & Diagnostics (Electronics Engineering) Solved Questions & Notes (2026) - Apex Rankers

Engineering & Technology > Electronics Engineering > PCB Inspection & Diagnostics

14 Total Solved Questions
~21 mins Estimated Reading Time
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PCB Inspection & Diagnostics

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Q. 1 Electronics Engineering
Difficulty: Medium (1 Mark)
In PCB manufacturing and quality inspection, what does the term 'tombstoning' refer to in surface-mount technology (SMT)?
A
A chip component (resistor/capacitor) lifting on one end during reflow soldering due to unbalanced surface tension
✓ Correct
B
Complete delamination of inner copper planes
C
Oxidation of gold plated edge contacts
D
Thermal runaway of power transistors
💡 Step-by-Step Explanation & Concept Rationale
Tombstoning (the Manhattan effect) occurs when uneven heating or unequal solder pad geometry causes solder paste to melt faster on one end of a two-terminal chip component, pulling the component upright.
Q. 2 Electronics Engineering
Difficulty: Medium (1 Mark)
Which international standard specifies the acceptability criteria for electronic assemblies (soldering quality, component placement, cleanliness)?
A
IPC-A-610
✓ Correct
B
ISO 9001
C
IEEE 802.3
D
ANSI C84.1
💡 Step-by-Step Explanation & Concept Rationale
IPC-A-610 ('Acceptability of Electronic Assemblies') is the internationally recognized benchmark standard for visual quality acceptance of soldered electronic assemblies (Class 1, Class 2, Class 3).
Q. 3 Electronics Engineering
Difficulty: Easy (1 Mark)
What is the primary cause of damage to sensitive CMOS and MOSFET components during handling and board assembly?
A
Electrostatic Discharge (ESD)
✓ Correct
B
Ambient room lighting
C
Low atmospheric pressure
D
Normal audio acoustic vibrations
💡 Step-by-Step Explanation & Concept Rationale
Electrostatic Discharge (ESD) generates transient potentials of thousands of volts that puncture the microscopic thin gate oxides (SiO2) of MOSFETs and CMOS ICs, causing latent or catastrophic failure.
Q. 4 Electronics Engineering
Difficulty: Medium (1 Mark)
To safely protect electronic components against ESD damage, an ESD wrist strap must incorporate which safety feature for the human operator?
A
A 1-Megaohm current-limiting safety resistor in series with ground
✓ Correct
B
A direct zero-ohm copper braid connection to mains earth
C
A 10-ampere fast-acting fuse
D
A step-down isolating transformer
💡 Step-by-Step Explanation & Concept Rationale
ESD wrist straps always include a series 1 Mohm resistor. This allows static charges to safely bleed off to earth in milliseconds while protecting the wearer against lethal electrical shock if they accidentally touch mains voltage.
Q. 5 Electronics Engineering
Difficulty: Medium (1 Mark)
In multilayer PCB design, what is the purpose of placing dedicated, unbroken ground and power planes adjacent to signal layers?
A
To increase PCB mechanical weight
B
To provide low-inductance return current paths, minimize loop area, and suppress EMI/crosstalk
✓ Correct
C
To allow higher soldering temperatures during manual rework
D
To eliminate the need for surface-mount components
💡 Step-by-Step Explanation & Concept Rationale
Solid plane layers provide minimal impedance return paths directly beneath high-speed signal traces, minimizing current loop areas and dramatically reducing electromagnetic radiation (EMI) and crosstalk.
Q. 6 Electronics Engineering
Difficulty: Easy (1 Mark)
What type of non-destructive diagnostic technique is used to inspect solder joints beneath Ball Grid Array (BGA) components on a PCB?
A
X-ray inspection (Automated X-ray Inspection - AXI)
✓ Correct
B
Optical microscope
C
UV blacklight dye penetration
D
Ultrasonic immersion bath
💡 Step-by-Step Explanation & Concept Rationale
Because BGA solder balls are hidden underneath the component package body, X-ray inspection (AXI) is required to detect solder bridging, voids, cold solder joints, and missing balls.
Q. 7 Electronics Engineering
Difficulty: Easy (1 Mark)
In troubleshooting printed circuit boards, what is the function of a 'thermal camera' or infrared imaging?
A
To identify shorted components, failing bypass capacitors, or overloaded ICs that generate localized hot spots
✓ Correct
B
To measure high-frequency clock jitter
C
To verify the firmware version inside flash memory
D
To clean solder flux residue from pads
💡 Step-by-Step Explanation & Concept Rationale
Infrared thermal cameras quickly pinpoint shorted decoupling capacitors, internal silicon shorts, or excessive current draw by showing distinct temperature elevations (hot spots).
Q. 8 Electronics Engineering
Difficulty: Medium (1 Mark)
What is the recommended lead-free solder alloy composition commonly used in electronics assembly under RoHS compliance?
A
60% Tin / 40% Lead (Sn60/Pb40)
B
SAC305 (96.5% Tin, 3.0% Silver, 0.5% Copper)
✓ Correct
C
50% Lead / 50% Indium
D
90% Cadmium / 10% Zinc
💡 Step-by-Step Explanation & Concept Rationale
Under RoHS directives banning lead (Pb), SAC305 (Sn96.5 Ag3.0 Cu0.5) is the most widely adopted lead-free solder alloy in surface mount manufacturing, with a melting point around 217°C.
Q. 9 Electronics Engineering
Difficulty: Hard (1 Mark)
What does JTAG (Joint Test Action Group - IEEE 1149.1) boundary-scan technology enable in modern electronic board testing?
A
Testing of pin-to-pin interconnects, shorts, opens, and in-system programming of ICs without physical probe contact on pins
✓ Correct
B
Measuring analog RF noise figure in microwave receivers
C
Increasing PCB trace current-carrying capacity by 200%
D
Generating clock signals for external switched-mode power supplies
💡 Step-by-Step Explanation & Concept Rationale
IEEE 1149.1 boundary-scan embeds shift-register cells at each I/O pin of ICs, allowing digital testing of continuity, traces, opens, and shorts, and firmware flashing via a simple 4- or 5-wire JTAG port.
Q. 10 Electronics Engineering
Difficulty: Easy (1 Mark)
What is the function of a decoupling (bypass) capacitor placed immediately adjacent to the Vcc pin of an integrated circuit?
A
To act as a high-frequency energy reservoir and shunt high-frequency switching noise to ground, stabilizing supply voltage
✓ Correct
B
To increase the DC supply voltage to twice its value
C
To provide reverse polarity battery protection
D
To delay the clock signal by 90 degrees
💡 Step-by-Step Explanation & Concept Rationale
During rapid transistor switching, ICs draw instantaneous surge currents. Decoupling capacitors (e.g. 100 nF ceramic) supply this transient charge locally, preventing voltage rail dips and radiated noise.
Q. 11 Electronics Engineering
Difficulty: Medium (1 Mark)
What happens when a high-speed digital signal trace on a PCB encounters a sharp 90-degree bend or a split in the underlying ground plane?
A
The trace impedance is unaffected and EMI is reduced
B
An impedance discontinuity is created, causing signal reflections, increased EMI, and trace inductance changes
✓ Correct
C
The signal propagation velocity increases to infinity
D
The logic voltage level automatically doubles
💡 Step-by-Step Explanation & Concept Rationale
Trace width changes or passing over plane splits disrupts characteristic impedance (Z0), creating signal reflections, ringing, increased return path loop area, and severe electromagnetic emissions.
Q. 12 Electronics Engineering
Difficulty: Medium (1 Mark)
Which type of flux residue is corrosive and MUST be washed off with water immediately following PCB soldering?
A
No-clean rosin flux
B
Water-soluble (organic acid) flux
✓ Correct
C
Pure beeswax flux
D
Mildly activated rosin (RMA) flux
💡 Step-by-Step Explanation & Concept Rationale
Water-soluble (OA - Organic Acid) fluxes contain highly active organic acids that provide excellent wetting but will aggressively corrode copper traces and component leads if not thoroughly washed with deionized water.
Q. 13 Electronics Engineering
Difficulty: Medium (1 Mark)
In printed circuit board testing, what is the purpose of an 'In-Circuit Test' (ICT) bed-of-nails fixture?
A
To optically scan QR barcodes on PCB boards
B
To verify individual passive component values (R, L, C), diode orientations, and detect board shorts/opens using spring-loaded pogo pins
✓ Correct
C
To heat-treat the board inside an environmental oven
D
To measure cosmic ray absorption in outer space applications
💡 Step-by-Step Explanation & Concept Rationale
In-Circuit Testing (ICT) utilizes an array of spring-loaded test pins ('bed of nails') contacting dedicated test pads to measure discrete component values, shorts, opens, and orientation before functional testing.
Q. 14 Electronics Engineering
Difficulty: Easy (1 Mark)
What is the primary indicator of a cold (dry) solder joint during manual visual inspection?
A
A smooth, bright, concave shiny wetting meniscus
B
A dull, grainy, greyish appearance with cracks or poor wetting around the lead
✓ Correct
C
A completely golden mirror finish
D
A translucent glass-like coating over the lead
💡 Step-by-Step Explanation & Concept Rationale
Cold solder joints (caused by insufficient heat, movement during cooling, or contaminated surfaces) exhibit a dull, grainy, cracked, or chalky surface with poor wetting that creates intermittent contact.
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