CIS Electronic Assembly & Manufacturing Processes 3 — Questions and Answers
Question 1: Which flux type leaves the least residue and typically does not require post-solder cleaning?
- Water-soluble flux
- No-clean flux (Correct answer)
- Rosin flux (RMA)
- Organic acid flux
Correct answer: No-clean flux
No-clean flux is formulated to leave minimal, non-corrosive residue that does not require cleaning after soldering.
Question 2: What is the role of aperture design in stencil printing for SMT assembly?
- Determine conveyor belt speed
- Control the volume and location of solder paste deposited (Correct answer)
- Set the reflow temperature profile
- Define component orientation
Correct answer: Control the volume and location of solder paste deposited
Stencil apertures define the shape, size, and position of solder paste deposits, directly controlling paste volume on each pad.
Question 3: During wave soldering, what is the function of the preheater section?
- Melt solder in the bath
- Activate flux and bring the board near soldering temperature (Correct answer)
- Cool the board after soldering
- Apply solder mask
Correct answer: Activate flux and bring the board near soldering temperature
The preheat section activates flux, evaporates solvents, and raises PCB temperature to reduce thermal shock during wave contact.
Question 4: What is a 'voiding' defect in solder joints?
- Missing solder on a pad
- Gas pockets trapped inside a solder joint (Correct answer)
- Excess solder bridging two pads
- Lifted pads from the substrate
Correct answer: Gas pockets trapped inside a solder joint
Voiding refers to gas or vapor pockets trapped within a solidified solder joint, which can weaken mechanical and electrical performance.
Question 5: Which process uses localized heat to solder individual through-hole components while protecting SMT components on the same board?
- Reflow soldering
- Dip soldering
- Selective soldering (Correct answer)
- Vapor phase soldering
Correct answer: Selective soldering
Selective soldering applies solder only to designated areas using a miniature solder wave or laser, protecting nearby SMT components.
Question 6: In IPC-A-610, what are the three condition categories used to classify solder joint acceptability?
- Pass, Marginal, Fail
- Target, Acceptable, Defect (Correct answer)
- Class 1, Class 2, Class 3
- Good, Rework, Reject
Correct answer: Target, Acceptable, Defect
IPC-A-610 classifies conditions as Target (ideal), Acceptable (meets minimum requirements), or Defect (rejectable condition).
Question 7: What is the purpose of a soldering iron tip's tinning process during hand soldering?
- Clean the iron barrel of oxidation
- Coat the tip with fresh solder to improve heat transfer (Correct answer)
- Reduce tip temperature
- Remove flux residue
Correct answer: Coat the tip with fresh solder to improve heat transfer
Tinning a soldering iron tip coats it with a thin layer of solder, improving thermal contact and protecting the tip from oxidation.
CIS Electronic Assembly & Manufacturing Processes 3
Which flux type leaves the least residue and typically does not require post-solder cleaning?