PCB Assembly Checklist

This checklist is prepared to ensure control of hardware, materials, static protection, and special processes that may be overlooked during printed circuit board assembly. It should be used together with assembly instructions to ensure the design is transferred to the production line completely.

Bill of Materials (BOM) and Hardware Items​

1. Are all auxiliary parts listed in the BOM?​

All auxiliary and mechanical parts other than electronic components should be clearly defined in the bill of materials (BOM). This list should include screws, nuts, washers, heat sinks, thermal pastes, insulation washers, IC sockets, solder wire, acrylic protective coatings, labels, and assembly accessories. Lack of these parts leads to interruptions in the production line and quality problems. Complete BOM is a fundamental requirement for continuity of the assembly process.

2. Are assembly notes created for all hardware parts?​

Assembly notes should be prepared for all non-electronic components. These notes should specify the placement position of parts, tightening torque, orientation, connection sequence, and any special warnings (e.g., "insulation washer must be used", "heat sink paste should be applied in thin layer"). Assembly notes serve as reference documents for both operators and quality control personnel. Additionally, this information provides traceability in post-production rework or service processes.

Special Assembly Operations​

3. Are explanatory instruction notes added for all special assembly operations?​

All steps requiring non-standard or special operations during assembly should be documented with explanatory instruction notes. These operations may include: screw or press mechanical assemblies, thermal paste or insulation washer applications, torque-controlled tightening operations, special soldering methods (e.g., wave soldering, selective soldering), or pre-heating steps before soldering. These instructions are critically important for both production line operators and quality control teams to perform correct and repeatable operations. These special notes should be clearly indicated on schematics or assembly drawings, and related reference pages or document codes should be added if available.

4. Are assembly sequence and routing instructions determined?​

The sequence and routing logic for placing components during assembly should be planned in advance. For example, high-temperature or bulky components (heat-sinked regulator, transformer, connector) should be mounted before other components. This provides ease of access during soldering, reduces rework requirements, and shortens assembly time. Also, if there are assemblies on both sides of the board, top and bottom assembly sequences should be specified in production documents. Proper definition of assembly sequence directly increases production efficiency in terms of both heat profile optimization and mechanical integrity.

Coating and Protection Processes​

5. Is there a conformal coating requirement?​

If conformal coating application is required according to the board's operating environment, this requirement should be clearly stated in production documents. Coating increases the board's insulation resistance and durability in moisture, dust, chemical vapors, or salty environments. Before application, the following information should be clearly defined: Areas to be coated (e.g., power stage, analog circuit, high voltage area), Areas to be masked (e.g., connector, potentiometer, test pad, mechanical contact surface), Coating material to be used (e.g., acrylic, silicone, polyurethane, parylene), Application method (spray, brush, dip, or vacuum). This information prevents confusion on the production line and ensures quality standard maintenance. Coating type should also be selected for reworkability; for example, acrylic coatings provide repair ease while parylene offers high protection.

6. Are areas not to be coated clearly marked?​

Areas to be masked during conformal coating process should be clearly defined. Connectors, test points, mounting holes, potentiometers, and mechanical interfaces (e.g., heat sink contact areas) should be left outside coating. Areas to be masked should be shown as coating keep-out layer in production file and physically described to the manufacturer. Incorrect coating can block test access or create contact problems at mechanical connection points. Therefore, preparing a separate document called "Coating Map" or "Masking Drawing" is recommended.

Electrostatic Discharge (ESD) and Assembly Safety​

7. Are ESD protection requirements clearly stated in assembly notes?​

For all ESD-sensitive circuit boards, static protection warnings should be clearly included in assembly and test documents. For example: "This board is ESD sensitive. Use antistatic wrist strap, floor mat, and ionizing air gun." These warnings should be visible both in assembly area and at test/quality control stations. ESD protection notes are critically important not only for production safety but also for warranty and quality certification processes. This information should appear both in PCB assembly drawings and external packaging labels.

8. Are proper labeling and packaging done for ESD sensitive components?​

Before assembly, all ESD sensitive components should be stored in antistatic bags or conductive packaging materials. The package should have ESD warning label (yellow/black triangle symbol) and component code. Additionally, use of humidity indicator cards and desiccant packs in component storage areas is recommended. Improper packaging can cause components to be damaged before reaching the production line.

9. Does assembly line personnel have ESD equipment and are grounding tests performed regularly?​

ESD protection is ensured not only by design but also by process discipline. Personnel working on the assembly line must use protective equipment such as: Antistatic wrist strap, Grounded floor mat, Antistatic shoes or heel strap, Ionizing air systems. Additionally, grounding continuity tests of this equipment should be performed regularly. ESD discharges from grounding failures can cause microscopic damage in integrated circuits. These checks should generally comply with ISO 61340 or ANSI/ESD S20.20 standards.

General Application and Documentation​

10. Are explanatory symbols or references used in assembly drawings for special operations?​

Explanatory symbols or abbreviations should be used in assembly documents for steps requiring special operations. These visual codes facilitate readability on the production line and reduce the possibility of operator errors. Example usage: COAT → Area where conformal coating will be applied, ESD → Component requiring static protection, TORQ → Screw connection requiring torque control, GLUE → Area where adhesive will be applied. These symbols should be provided with an explanation table in assembly drawings or "Assembly Instruction Sheet" document.

11. Is post-assembly quality control checklist defined?​

After assembly completion, a checklist to be applied by the quality team should be defined. Main items to be checked in this list: Proper seating and full contact of heat sinks, Proper placement of insulation washers without compression, Correct application of conformal coating areas, Complete attachment of ESD labels, Appropriateness of torque values. These checks should be performed with both visual inspection and dimensional verification.

12. Are labels and markings on the board verified after assembly completion?​

All labels and identification markings that should be present on the board after assembly should be checked. These include: Revision label, Serial number, Production date / date code, ESD warning label, Quality control stamp (QC Passed). It should be ensured that these labels are attached in the correct position and permanently. Missing or incorrect labels weaken traceability processes.

13. Is reflow profile and MSL (Moisture Sensitivity Level) information defined?​

Moisture sensitivity level (MSL) specified by the manufacturer for all SMD components used should be included in assembly document. Pre-baking process for components especially MSL 3 and above should be specified with duration and temperature values. Reflow profile should include parameters such as maximum peak temperature, heating rate (ramp rate), and cooling curve. This information should comply with both manufacturer recommendations and JEDEC J-STD-020 standard.

14. Is X-ray / BGA inspection step defined?​

X-ray inspection step should be specified in production plan for components with bottom leads such as BGA, LGA, or QFN. This inspection is mandatory to detect hidden solder defects (void, short, open). X-ray test results should be added to quality report as reference. This check is a standard requirement in products requiring high reliability (automotive, medical, aerospace).

15. Is solder paste stencil thickness and aperture ratio specified?​

In assembly drawings or production notes, thickness (e.g., 100–150 µm) and aperture opening ratio (50–90%) related to solder paste stencil should be specified. Incorrect stencil thickness can cause solder bridges or insufficient solder formation. Stencil data should be verified through "Gerber Paste Layer" in agreement with manufacturer.

16. Are board position reference markers (fiducials) verified for AOI and ICT test stations?​

Fiducial markers to be used for AOI (Automatic Optical Inspection) and ICT (In-Circuit Test) systems should be in correct position on the board. Fiducials should be defined with maskless copper surface around them, clear enough to be detected by machine camera. Missing or misaligned fiducials lead to alignment errors in testing process.

17. Is post-assembly cleaning and drying procedure added?​

After assembly completion, flux residues, solder paste residues, or contaminants remaining on the board should be cleaned with appropriate solvent or ultrasonic washing method. Drying time and temperature value after cleaning should be specified (e.g., 1 hour at 60°C). This step prevents long-term surface corrosion and leakage currents. After cleaning, boards should be stored in antistatic bags.