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Soldering Techniques & Standards Flashcards

7 cards from real CIS practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.

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  1. The RoHS Directive primarily restricts which substance in solder alloys used in electronics?

    Answer: Lead (Pb)

    RoHS (Restriction of Hazardous Substances) restricts lead (Pb) and five other hazardous substances, driving the industry shift to lead-free solder alloys.

  2. 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.

  3. What is the approximate melting point difference between eutectic Sn63/Pb37 solder and SAC305 lead-free solder?

    Answer: Approximately 34°C higher for SAC305 (183°C vs ~217°C)

    Eutectic Sn63/Pb37 melts at 183°C, while SAC305 has a liquidus of approximately 217–221°C, requiring higher process temperatures.

  4. When mixing lead-free BGAs onto a leaded solder paste assembly (a 'backward compatibility' scenario), what is the primary reliability risk?

    Answer: Fillet lifting and insufficient intermetallic formation due to higher Pb-contamination in the joint

    Lead migrating from paste into the Pb-free ball can create low-melting-point phases and fillet lifting, compromising joint reliability under thermal cycling.

  5. Per IPC/JEDEC J-STD-020, what does Moisture Sensitivity Level (MSL) 3 indicate for a component?

    Answer: Floor life of 168 hours at ≤30°C/60% RH before reflow soldering is required

    MSL 3 components have a 168-hour (one week) floor life at ambient conditions of ≤30°C/60% relative humidity before mandatory baking or soldering.

  6. What is 'head-in-pillow' (HiP) defect in BGA soldering and what primarily causes it?

    Answer: The solder ball and paste solder solidify separately without fully coalescing, often due to oxidation or insufficient flux activity at peak temperature

    HiP occurs when the ball and paste fail to merge during reflow, creating a non-wetted interface that may pass visual/X-ray inspection but fails electrically.

  7. Which lead-free alloy is specifically chosen for step soldering lower-temperature assemblies after higher-temperature joints are already made?

    Answer: SnBi (Sn42/Bi58) with a melting point of ~138°C

    SnBi eutectic alloy melts at approximately 138°C, making it ideal for step soldering where lower heat prevents remelting of previously made higher-temperature joints.