CIS CIS Acceptability Criteria & Defect Recognition 2 — Questions and Answers
Question 1: What is 'tombstoning' in the context of SMT assembly?
- A type of solder bridge between adjacent pads
- A defect where one end of a chip component lifts off its pad during reflow (Correct answer)
- Excessive solder forming a columnar shape on a pad
- A component placed at 90° to its intended orientation
Correct answer: A defect where one end of a chip component lifts off its pad during reflow
Tombstoning (also called drawbridging) occurs when one end of a small chip component lifts during reflow due to unequal surface tension forces on the solder.
Question 2: According to IPC-A-610, component skew for chip resistors and capacitors is acceptable for Class 2 when:
- The component is rotated no more than 45°
- Both terminations remain on their respective pads within specified limits (Correct answer)
- The component does not touch adjacent components
- No skew is acceptable for Class 2
Correct answer: Both terminations remain on their respective pads within specified limits
For Class 2, component skew is acceptable as long as both terminations remain on their pads within the allowable placement offset limits specified for the component type.
Question 3: What defect is described as solder that forms a sharp peak or spike projecting from a solder joint?
- Solder balling
- Solder icicle (solder spike) (Correct answer)
- Solder skip
- Webbing
Correct answer: Solder icicle (solder spike)
A solder icicle or solder spike is a sharp protrusion of solder projecting from the joint, which can cause shorts if it contacts adjacent conductors.
Question 4: For IPC-A-610, what is the acceptability status of a solder ball that is NOT entrapped under a component and can be removed without damaging the assembly?
- Always acceptable for all classes
- Defect for Class 3 only
- Defect for Class 2 and Class 3
- Process indicator for Class 1, defect for Class 2 and 3 (Correct answer)
Correct answer: Process indicator for Class 1, defect for Class 2 and 3
Solder balls not trapped under components are a process indicator for Class 1 and a defect for Class 2 and Class 3 assemblies per IPC-A-610.
Question 5: 'Dewetting' in soldering refers to:
- Solder that has not melted sufficiently during the soldering process
- Solder that wetted a surface but then partially pulled back, leaving an uneven, irregular surface (Correct answer)
- A base metal surface that has been oxidized prior to soldering
- The process of removing flux residue after soldering
Correct answer: Solder that wetted a surface but then partially pulled back, leaving an uneven, irregular surface
Dewetting occurs when solder initially wets a surface but then contracts or pulls back, leaving irregular solder masses separated by areas where the base metal is exposed.
Question 6: According to IPC-A-610, which condition constitutes a defect for all classes regarding component body damage?
- Minor surface scratches on the component body
- Cracking that exposes internal component material (Correct answer)
- Discoloration of the component body from heat
- Damaged component markings that are still partially readable
Correct answer: Cracking that exposes internal component material
Cracking that exposes the internal material of a component body is a defect for all IPC classes because it compromises component integrity and reliability.
CIS CIS Acceptability Criteria & Defect Recognition 2
What is 'tombstoning' in the context of SMT assembly?