CIS Electronic Assembly & Manufacturing Processes 2 — Questions and Answers
Question 1: Which soldering defect is characterized by solder forming a bridge between two adjacent pads without wetting properly?
- Cold joint
- Solder bridging (Correct answer)
- Tombstoning
- Voiding
Correct answer: Solder bridging
Solder bridging occurs when excess solder connects two adjacent pads or leads, creating an unintended electrical short.
Question 2: What is the primary purpose of nitrogen atmosphere in a reflow oven?
- Increase conveyor speed
- Reduce oxidation of solder and pads (Correct answer)
- Lower peak temperature
- Improve flux activation
Correct answer: Reduce oxidation of solder and pads
Nitrogen atmosphere displaces oxygen, preventing oxidation of molten solder and PCB pads during reflow soldering.
Question 3: In through-hole technology, what process is used to fill plated through-holes with solder from the bottom side of a PCB?
- Reflow soldering
- Wave soldering (Correct answer)
- Selective soldering
- Hand soldering
Correct answer: Wave soldering
Wave soldering passes the bottom of the PCB over a wave of molten solder to simultaneously solder all through-hole leads.
Question 4: Which component placement defect occurs when a chip component stands on one end due to uneven solder paste wetting?
- Skewing
- Tombstoning (Correct answer)
- Shadowing
- Sliverting
Correct answer: Tombstoning
Tombstoning (also called drawbridging) happens when one end of a component lifts up due to unbalanced surface tension forces during reflow.
Question 5: What is the recommended approach when reworking a BGA component according to IPC standards?
- Replace with hand-soldered wires
- Use approved rework station with profiled heat (Correct answer)
- Reflow the entire board again
- Apply additional flux and press down
Correct answer: Use approved rework station with profiled heat
BGA rework requires a specialized rework station that applies profiled heat to reflow solder balls without damaging adjacent components.
Question 6: Which IPC standard specifically addresses the acceptability of electronic assemblies?
- IPC-A-600
- IPC-A-610 (Correct answer)
- IPC-7711
- IPC-2221
Correct answer: IPC-A-610
IPC-A-610, Acceptability of Electronic Assemblies, is the most widely used electronics assembly standard defining workmanship criteria.
Question 7: What does the term 'tombstoning' describe in SMT assembly?
- Solder mask delamination
- A component lifted vertically on one end (Correct answer)
- Voids beneath a pad
- Solder overflow onto via holes
Correct answer: A component lifted vertically on one end
Tombstoning is an SMT defect where one end of a chip component lifts off the pad during reflow due to unequal surface tension forces.
CIS Electronic Assembly & Manufacturing Processes 2
Which soldering defect is characterized by solder forming a bridge between two adjacent pads without wetting properly?