Comprehensive Soldering Project: Build, Inspect, and Document a Functional PCB
Objective. The learner will solder a complete functional electronic assembly (mixed through-hole and SMT) from a bill of materials, perform a full IPC-A-610 self-inspection, and verify functionality with a multimeter and power-up test, producing a completed inspection traveler.
This lesson, its worked examples and its practice questions has not yet been verified by an industry-certified professional or by a certification or approval body. It is a study draft and may contain errors. Do not use it as instructions for work on a job site or on live equipment. Always follow your instructor, your supervising professional, and current official references and regulations.
VoTechWorks program approval and accreditation are still in progress. Credentials are issued only by the certifying bodies named in each program, after their own exams.
Overview: The Capstone Soldering Lab
This lab brings together every skill you have practiced in this course. You will kit your own components, build a mixed-technology PCB (surface-mount technology first, then through-hole, then wire harness), inspect your work to IPC-A-610 Class 2, and demonstrate that the board works. The finished board plus a fully signed inspection traveler are your deliverables.
Safety First
Before picking up a soldering iron, review these non-negotiable rules:
- Burns and fire. Soldering irons reach 600 °F or more. Always return the iron to its holder when not in your hand. Never reach across a powered station.
- Fumes. Rosin and flux fumes are respiratory irritants. Work at or near a fume extractor; never put your face over a joint being soldered.
- PPE. Safety glasses are required at all times during soldering, clipping leads, or using hot air. Lead-free SAC305 solder still contains tin and silver—wash hands before eating or touching your face.
- Hot-air hazards. Hot-air stations can ignite nearby flux residue or damage adjacent components if aimed carelessly. Keep the nozzle moving and clear of plastics.
- ESD. Many components in this kit are ESD-sensitive. Use your wrist strap and ESD mat throughout the lab.
- Bench power supply. When powering up, start at the minimum voltage specified by the acceptance spec, confirm polarity, and increase slowly. Never exceed the rated voltage of the kit.
Step 1: Kitting and BOM Verification
Professional assembly always starts at the stockroom, not at the iron. Pick up your kit bag and assembly drawing, then verify every component against the bill of materials (BOM) line by line:
1. Count quantity against the BOM quantity column.
2. Read or measure each component's value (resistor color codes, capacitor markings, IC part numbers).
3. Check polarity markings on diodes, electrolytic capacitors, and ICs.
4. Record any discrepancy on the lab log before proceeding—never assume a substitution is acceptable without instructor approval.
Also study the assembly drawing now to plan your sequence. The rule is SMT before through-hole because SMT reflow requires a flat, component-free board surface and oven or hot-air temperatures that would damage installed through-hole parts with plastic bodies.
Step 2: SMT Assembly
Apply flux to SMT pads. Place components using tweezers, checking orientation marks on ICs and polarized capacitors against the silkscreen. For hot-air reflow, set your station to the solder paste or solder wire manufacturer's recommended peak temperature—for SAC305, the liquidus point is 217 °C (423 °F), so a tip or air temperature of roughly 320–370 °C is typical for small SMT work; follow your station's documented setting for the component mass you are soldering. Work methodically across the board; log your temperature setting in the lab log before you begin and note any rework.
Inspect SMT joints before proceeding. Look for: bridging between pads, tombstoning (one end lifts), insufficient wetting, or excess solder. Correct defects now—rework is far easier before through-hole parts are installed.
Step 3: Through-Hole Assembly
Insert through-hole parts in the sequence shown on the assembly drawing, generally shortest to tallest to allow the board to lie flat while you solder. Bend leads slightly after insertion so parts do not fall out when you flip the board. Apply iron tip to both the lead and the pad simultaneously for approximately two to three seconds, feed solder to the joint (not the iron), then remove solder and iron in sequence. A correct through-hole joint is shiny (SAC305 may be slightly matte compared with tin-lead—this is normal), volcano-shaped, and shows solder wicking up the barrel.
Trim excess lead length with flush-cut diagonal cutters; wear your safety glasses—cut leads are projectiles.
Step 4: Wire Harness Connections
If the kit includes a wire harness, strip to the length specified on the assembly drawing (typically 5–7 mm for soldered connections), tin the wire end, then solder to the designated pads or connector. Polarity errors in harness connections are a common and potentially destructive mistake—verify wire color against the drawing before soldering.
Step 5: IPC-A-610 Class 2 Self-Inspection
IPC-A-610 defines three classes of acceptability. Class 2 (general electronics) is the standard for most telecom and industrial products. Using your copy of the IPC-A-610 reference and a magnifying loupe if available, evaluate every joint and record the result on the inspection traveler:
- Acceptable: joint meets all geometric and wetting criteria.
- Process indicator: a condition worth noting but not a defect.
- Defect: a condition that must be corrected before the board can be accepted.
Common Class 2 defects to look for: insufficient solder fill in through-hole barrels (less than 75% fill is a defect), solder bridges, lifted pads, poor wetting (dull, grainy, or non-wetted surface), component misalignment beyond Class 2 tolerances, and damaged component bodies.
Document every finding—joint reference, condition, and disposition (accept or rework)—on the traveler. Date and sign the self-inspection section.
Step 6: Functional Test
With the instructor's acceptance spec in hand:
1. Set the bench power supply to the specified voltage and current limit.
2. Confirm polarity at the board power connector.
3. Power up and observe the acceptance criteria (LED illumination, measured output voltage, frequency, or continuity reading as specified).
4. Record measured values on the traveler.
If the board fails functional test, use your multimeter to locate the fault (check supply voltage at the board, then trace the signal path), correct, re-inspect the rework, and retest.
Final Sign-Off
Present your board and completed traveler to the instructor. The instructor will perform an independent IPC-A-610 Class 2 inspection. Acceptance requires ≥ 95% of all joints accepted and a passing functional test. Any Class 2 defect identified by the instructor must be reworked, documented, and re-inspected before the traveler is signed off.
Key terms10
Worked examples3
- Recall the IPC-A-610 Class 2 minimum barrel fill requirement: 75% fill is the minimum acceptable condition.
- Compare the measured/estimated fill (60%) to the requirement (75%).
- 60% is less than 75%, so the condition falls below the Class 2 minimum.
- Classify the joint: this is a Class 2 defect because it does not meet the minimum fill criterion.
- Determine required action: defects must be reworked. Apply additional solder to the joint, reheat until solder flows fully into the barrel, allow to cool, and re-inspect.
- Identify the liquidus temperature of SAC305: 217 °C.
- Apply the low end of the superheat margin: 217 °C + 100 °C = 317 °C.
- Apply the high end of the superheat margin: 217 °C + 150 °C = 367 °C.
- Confirm this falls within typical hot-air station guidance for small SMT components (roughly 320–370 °C is common in practice; 317–367 °C aligns with this range).
- Log the chosen setting (within 317–367 °C) in the lab log before beginning reflow.
- Identify total joints: 80.
- Identify defective joints: 4.
- Calculate accepted joints: 80 − 4 = 76.
- Calculate acceptance percentage: (76 ÷ 80) × 100 = 95.0%.
- Compare to the threshold: 95.0% meets the ≥95% requirement exactly.
- However, all Class 2 defects must still be reworked per IPC-A-610 policy regardless of the percentage—they are defects by definition and cannot be left on an accepted board.
The math in this lesson1
Materials: Kitted functional PCB assembly (instructor-designed or commercially available educational kit—e.g., a signal generator or LED driver PCB), complete BOM and assembly drawing, temperature-controlled iron, hot-air station, SAC305 solder, flux pen, digital multimeter, DC bench power supply (if required by kit), IPC-A-610 reference, lab log, inspection traveler form
Check: Inspector (instructor) performs independent IPC-A-610 Class 2 inspection of completed board: ≥95% of all joints accepted. Board must pass functional test as defined by kit acceptance spec. Inspection traveler must be fully filled out and signed. Any Class 2 defect requires documented rework before final sign-off.
Practice check8
Answer each question, then check it. Nothing is recorded; this is your own practice.
