Mixed Deck — All CIS Topics Flashcards

The most common lead-free solder alloy used in SMT reflow soldering per J-STD-006 is:

Answer: SAC305 (Sn96.5/Ag3.0/Cu0.5)

SAC305 (96.5% tin, 3% silver, 0.5% copper) is the industry-standard lead-free alloy with a melting point of approximately 217–221°C.

Which cleanliness test method measures ionic contamination on a PCB assembly after soldering?

Answer: ROSE (Resistivity of Solvent Extract) test

The ROSE test (also known as the Omega-meter test) measures ionic contamination by dissolving surface residues in isopropyl alcohol/water and measuring resistivity change.

What is 'pad conditioning' during SMT rework?

Answer: Cleaning, re-tinning, or reshaping the solder pad to its proper form before installing a replacement component

Pad conditioning involves cleaning residual solder from the pad, re-tinning with fresh solder if needed, and verifying the pad shape and condition before installing a replacement component.

An inspector observes a solder bridge between two adjacent SMD pads on a Class 2 assembly. Which of the following best describes the disposition?

Answer: Defect — requires rework or rejection

Solder bridges between conductors that should not be electrically connected are unconditional defects under IPC-A-610 for all product classes.

When performing solderability testing per J-STD-003, what does the wetting balance test measure?

Answer: The force exerted on a component lead as it is immersed in molten solder

The wetting balance (Meniscograph) test measures the time-force curve as a lead is immersed in solder, quantifying the speed and degree of solder wetting.

What hazard does halide contamination (chlorides, bromides) pose to PCB assemblies?

Answer: Halides are aggressive activators that accelerate corrosion and electrochemical migration if not fully removed

Halide ions (Cl⁻, Br⁻) from flux activators are aggressive corrosion catalysts; if left on the assembly, they absorb moisture and create highly corrosive ionic solutions that accelerate metal corrosion and electrochemical migration.

Which component placement defect occurs when a chip component stands on one end due to uneven solder paste wetting?

Answer: Tombstoning

Tombstoning (also called drawbridging) happens when one end of a component lifts up due to unbalanced surface tension forces during reflow.

What type of solder void is considered most critical and typically a defect in BGA joints per IPC-7095?

Answer: Voids exceeding 25% of the ball diameter located at the interface

IPC-7095 classifies voids greater than 25% of ball diameter, especially at the component or board interface, as defects that compromise joint reliability.

What is a 'jumper wire' modification in PCB repair, and what IPC standard governs it?

Answer: A conductor added to a PCB to correct a wiring error or replace a damaged trace, governed by IPC-7711/7721

A jumper wire is an added conductor used to replace a damaged trace or correct a wiring error; IPC-7711/7721 provides specific requirements for acceptable jumper wire installation.

What does ESD-protective workstation bonding ensure during hand soldering operations?

Answer: The operator, soldering iron tip, and PCB are all at the same electrical potential to prevent discharge

ESD bonding equalizes potential between the operator, iron tip, and work surface so no electrostatic discharge can occur across the assembly being soldered.

What is the maximum acceptable solder mask intrusion into a solder joint on a through-hole component per IPC-A-610?

Answer: Solder mask cannot reduce the minimum annular ring

Solder mask intrusion is acceptable as long as it does not reduce the minimum required annular ring below acceptance criteria.

What is the purpose of a 'rinse purity monitor' in an aqueous cleaning system?

Answer: To continuously measure the ionic content of the final rinse water to ensure it is not recontaminating boards

A rinse purity monitor measures the conductivity or resistivity of final rinse water to ensure it hasn't accumulated enough ionic contamination to recontaminate boards exiting the cleaning system.

What conformal coating defect is described as small circular depressions or craters that expose the underlying substrate?

Answer: Fisheye (cratering)

Fisheyes or cratering are circular depressions caused by surface tension differences, often from contamination or silicone, that pull the wet coating away from a point and expose the substrate.

What does a yellow triangle with a hand symbol on component packaging indicate?

Answer: Electrostatic sensitive device (ESD)

The yellow triangle with a hand symbol is the ESD sensitivity symbol per ESDA/JEDEC standards, indicating the device is susceptible to electrostatic discharge damage.

According to IPC-A-610, what is the maximum allowable percentage of a solder joint's height that may be voided for Class 2 SMT components?

Answer: 25%

IPC-A-610 allows up to 25% voiding by area in solder joints for Class 2 assemblies when inspected by X-ray.

Why do most commercial conformal coatings contain fluorescent UV additives?

Answer: To allow visual verification of coating coverage using a UV black light

UV fluorescent tracers cause the coating to glow visibly under ultraviolet light, enabling inspectors to quickly identify coated versus uncoated areas during quality control inspection.

Which inspection method is best suited for detecting internal delamination within a multilayer PCB without destroying the board?

Answer: Scanning Acoustic Microscopy (SAM)

Scanning Acoustic Microscopy (SAM) uses ultrasound to detect internal delaminations, voids, and disbonds within multilayer PCBs non-destructively.

What characteristic of a tantalum capacitor's marking identifies its positive terminal?

Answer: A '+' symbol or stripe is marked near the positive terminal (anode)

Tantalum capacitors are polarized and marked with a '+' symbol or stripe near the positive (anode) terminal to ensure correct orientation and prevent catastrophic failure from reverse voltage.

A CIS inspector observes a through-hole lead that extends 0.5 mm beyond the secondary side of the board on a Class 3 assembly. Per IPC-A-610, this is:

Answer: A defect — lead protrusion is below the minimum

IPC-A-610 Class 3 requires a minimum lead protrusion of 0.5 mm (some versions specify slightly higher), so 0.5 mm is at the borderline — verify against the current revision, but insufficient protrusion is a defect.

Which IPC standard specifically addresses the qualification and performance requirements for conformal coating materials?

Answer: IPC-CC-830

IPC-CC-830 is the dedicated qualification and performance specification for electrical insulating compounds including conformal coatings, while IPC-A-610 covers acceptability of the finished assembly.