CIT Requirements for Soldered Electrical and Electronic Assemblies 3 — Questions and Answers
Question 1: Under IPC J-STD-001, which class of product has the MOST stringent soldering requirements?
- Class 1 (General Electronics)
- Class 2 (Dedicated Service Electronics)
- Class 3 (High Reliability Electronics) (Correct answer)
- Class 4 (Military Specification)
Correct answer: Class 3 (High Reliability Electronics)
Class 3 (High Reliability Electronics) has the most stringent requirements, covering equipment where continued performance is critical and downtime cannot be tolerated.
Question 2: What is the maximum allowable solder ball diameter per IPC J-STD-001 for Class 2 assemblies?
- 0.13 mm (0.005 in)
- 0.25 mm (0.010 in) (Correct answer)
- 0.38 mm (0.015 in)
- 0.50 mm (0.020 in)
Correct answer: 0.25 mm (0.010 in)
For Class 2 assemblies, solder balls must not exceed 0.13 mm (0.005 in) in diameter to be acceptable per IPC J-STD-001.
Question 3: In IPC J-STD-001, 'dewetting' is defined as a condition where:
- Solder fails to flow onto the base metal at all
- Solder initially wets the surface but then recedes, leaving an irregular mounded appearance (Correct answer)
- Solder is applied at too low a temperature
- The solder joint contains excessive flux residue
Correct answer: Solder initially wets the surface but then recedes, leaving an irregular mounded appearance
Dewetting occurs when molten solder coats a surface and then pulls back, leaving irregular mounds of solder with base metal exposed between them.
Question 4: What is the primary purpose of activated flux in the soldering process?
- To increase the melting point of solder
- To remove oxides from metal surfaces to allow proper wetting (Correct answer)
- To add mechanical strength to the solder joint
- To prevent ESD damage during assembly
Correct answer: To remove oxides from metal surfaces to allow proper wetting
Activated flux chemically removes oxide layers from metal surfaces, enabling the molten solder to wet and bond properly to the base metal.
Question 5: Per IPC J-STD-001, a solder bridge between two conductors that are supposed to be electrically isolated is classified as:
- A process indicator for Class 1 only
- A defect for all product classes (Correct answer)
- Acceptable if the bridge is less than 0.5 mm
- A manufacturing process indicator for Class 2
Correct answer: A defect for all product classes
A solder bridge between isolated conductors is a defect for all product classes (1, 2, and 3) because it creates an unintended electrical short circuit.
Question 6: Which lead-free solder alloy is most commonly specified as the industry standard replacement for Sn63Pb37?
- SnBi58
- SAC305 (Sn96.5Ag3Cu0.5) (Correct answer)
- SnZn9
- SnIn48
Correct answer: SAC305 (Sn96.5Ag3Cu0.5)
SAC305 (96.5% tin, 3% silver, 0.5% copper) is the most widely adopted lead-free solder alloy and is considered the industry-standard replacement for tin-lead solder.
Question 7: Per IPC J-STD-001, what is the consequence of using a soldering iron tip temperature that is excessively high?
- Improved solder flow and wetting
- Faster throughput with no quality impact
- Potential component damage, PCB delamination, and pad lifting (Correct answer)
- Elimination of need for flux
Correct answer: Potential component damage, PCB delamination, and pad lifting
Excessive soldering iron temperature can damage heat-sensitive components, cause PCB delamination, lift pads, and degrade solder joint integrity.
CIT Requirements for Soldered Electrical and Electronic Assemblies 3
Under IPC J-STD-001, which class of product has the MOST stringent soldering requirements?