{"id":3721,"date":"2023-08-14T11:06:09","date_gmt":"2023-08-14T03:06:09","guid":{"rendered":"https:\/\/www.jingpengpcb.com\/?p=3721"},"modified":"2026-10-02T19:45:44","modified_gmt":"2026-10-02T11:45:44","slug":"flexible-circuit-board-smt-inspection","status":"publish","type":"post","link":"https:\/\/www.jingpengpcb.com\/en\/blog\/flexible-circuit-board-smt-inspection\/","title":{"rendered":"What inspections need to be performed before surface-mount assembly of FPC flexible circuits?"},"content":{"rendered":"

Before performing surface-mount assembly on flexible printed circuits (FPCs), a series of inspections must be conducted to ensure the quality and reliability of the components and the printed circuit board. These inspections cover component solderability, pin coplanarity, and appearance, as well as the layout and dimensions of the printed circuit board (flexible board). At the same time, attention must be paid to operational details and safety measures to ensure that the entire SMT assembly process proceeds smoothly.<\/p>\n

\"What<\/p>\n

I. SMT Component Inspection<\/h2>\n
    \n
  1. Solderability Testing<\/strong>: Use stainless steel tweezers to grasp the component body, immerse it in a tin bath at 235\u00b15\u00b0C or 230\u00b15\u00b0C, and remove it after 2\u00b10.2 seconds or 3\u00b10.5 seconds. Inspect the solder adhesion on the solder terminals under a 20x microscope. The solder terminals of the components must have a solder coverage of 90% or higher.<\/li>\n
  2. Pin Coplanarity Check<\/strong>: SOT and SOIC leads must not be deformed; for multi-lead QFP devices with a lead pitch of less than 0.65 mm, the lead coplanarity must be less than 0.1 mm (as verified by optical inspection using a placement machine).<\/li>\n
  3. Visual Inspection<\/strong>: Visually inspect or use a magnifying glass to check the soldered ends or leads of components for oxidation or contamination. The rated values, specifications, part numbers, accuracy, and dimensions of the components must comply with the product\u2019s manufacturing requirements.<\/li>\n
  4. Cleaning and Inspection<\/strong>: For products requiring cleaning, component residues will not come off after cleaning and will not affect the performance or reliability of the components (as observed visually after cleaning).<\/li>\n<\/ol>\n

    II. Inspection of Printed Circuit Boards (Flexible Boards)<\/h2>\n
      \n
    1. Layout and Dimension Checks<\/strong>: The layout and dimensions of the pads, solder mask, screen printing, and through-holes on flexible printed circuits should comply with the design requirements for SMT printed circuit boards. For example, check whether the spacing between pads is appropriate, whether screen printing is applied to the pads, and whether there are through-holes in the pads.<\/li>\n
    2. Dimensional Inspection<\/strong>: The external dimensions of the flexible circuit boards must be consistent, and their external dimensions, positioning holes, reference marks, etc., must meet the requirements of the production line equipment.<\/li>\n
    3. Warpage Dimension Inspection<\/strong>: Flexible circuit boards are allowed to warp, but this must be kept within certain limits. The maximum allowable upward warpage is 0.2 mm per 50 mm of length; the maximum allowable downward warpage is 0.2 mm per 50 mm of length; or the maximum allowable warpage along the entire length of the flexible circuit board is 1.5 mm.<\/li>\n
    4. Pollution Inspection<\/strong>: Check whether the flexible circuit board is contaminated or damp.<\/li>\n<\/ol>\n

      III. Precautions for SMT Assembly<\/h2>\n
        \n
      1. Electrostatic Protection<\/strong>: SMT assembly technicians must wear an electrostatic wrist strap that has been inspected and found to be in good working order. Before inserting components, check each order\u2019s electronic components for defects such as incorrect or mixed parts, damage, deformation, or scratches.<\/li>\n
      2. Preparing the Materials<\/strong>: For through-hole circuit boards, electronic components must be prepared in advance, and care must be taken to ensure the correct polarity of the capacitors.<\/li>\n
      3. Quality Inspection<\/strong>: After the SMT printing process is complete, inspect the parts for defects such as missing components, reversed components, or misalignment, and transfer the good, soldered products to the next process.<\/li>\n
      4. Electrostatic Protection<\/strong>: Before beginning SMT assembly, please wear an antistatic wrist strap. The metal strip should lie flat against the skin of your wrist and remain properly grounded. Work with one hand at a time.<\/li>\n
      5. Inserting Metal Parts<\/strong>: You must wear finger cots when inserting metal components such as USB\/IF sockets, shielding covers, tuners, and Ethernet ports.<\/li>\n
      6. Component Insertion<\/strong>: Components must be inserted in the correct position and orientation; they must lie flat on the board, and tall components must be inserted into the K-pin position.<\/li>\n
      7. Nonconformance Report<\/strong>: If you find that the materials do not meet the specifications in the SOP and BOM, report this to your team or supervisor immediately.<\/li>\n
      8. Handle with care<\/strong>: Handle materials with care. Do not drop flexible circuit boards that have undergone the previous SMT process, as this may damage components. Do not allow crystal oscillators to fall.<\/li>\n
      9. Organizing the Workbench<\/strong>: Please tidy up your work surface before leaving for the day and keep it clean.<\/li>\n
      10. Follow the Rules<\/strong>: Strictly adhere to the work area rules. It is strictly prohibited to place products in the first-piece inspection area, waiting area, defective product area, repair area, or small parts area without authorization. Note any unfinished processes during shift handoffs.<\/li>\n<\/ol>\n

        The above outlines the inspections and precautions that must be taken prior to SMT assembly of flexible circuit boards. Ensuring compliance with these steps and regulations can effectively improve the quality and efficiency of the SMT assembly process.<\/p>\n

        Frequently Asked Questions<\/h2>\n

        Q1: Why is solderability testing necessary?<\/strong><\/h3>\n

        Solderability testing is conducted to ensure the quality of component soldering and to prevent unstable connections or even failures caused by poor soldering.<\/p>\n

        Q2: What is the impact of warpage on flexible circuit boards?<\/strong><\/h3>\n

        Keeping the warpage of flexible circuits within a certain range can prevent instability or damage during subsequent assembly.<\/p>\n

        Q3: Why should you wear an anti-static wrist strap?<\/strong><\/h3>\n

        Static electricity can damage electronic components, and wearing an anti-static wrist strap can effectively prevent static interference.<\/p>\n

        Q4: Why do you need to wear finger sleeves when inserting metal parts?<\/strong><\/h3>\n

        Wearing finger cots prevents direct contact between your fingers and metal components, thereby preventing contamination or the effects of static electricity on the components.<\/p>\n

        Q5: Why should components be handled with care?<\/strong><\/h3>\n

        Handling components with care can prevent unnecessary damage and ensure their integrity and reliability.<\/p>","protected":false},"excerpt":{"rendered":"

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