{"id":2908,"date":"2024-11-07T09:11:09","date_gmt":"2024-11-07T01:11:09","guid":{"rendered":"https:\/\/www.jingpengpcb.com\/?p=2908"},"modified":"2026-10-02T19:43:27","modified_gmt":"2026-10-02T11:43:27","slug":"circuit-board-compression","status":"publish","type":"post","link":"https:\/\/www.jingpengpcb.com\/en\/blog\/circuit-board-compression\/","title":{"rendered":"Common Issues and Solutions for the Laminating Process of Multilayer Printed Circuit Boards"},"content":{"rendered":"

There are many issues related to the lamination process of multilayer printed circuit boards that require further study and discussion, such as copper foil wrinkling, layer misalignment, resin voids, white edges and corners, delamination and bubbling, and uneven board thickness, among others.<\/p>\n

To resolve and improve these issues, it is necessary to have a clear understanding of the main materials used in the pressing process (the inner core board and PP) as well as the control points of the press, and to be familiar with their characteristics.<\/p>\n

\"Laminating<\/p>\n

Key Materials in the Laminating Process<\/h2>\n

A. Inner Core Panel<\/h3>\n

The inner core layer is a multilayer board core that has been etched to form the inner layer pattern. Before lamination, the inner core must first undergo a browning (or blackening) treatment. The purpose of this treatment is to increase the surface roughness of the inner copper foil, ensuring that the PP film bonds fully with the copper surface during lamination and improving the bond strength between the PP and the copper surface. As the number of layers in the multilayer board increases, the inner core sheets become thinner, and the process gradually shifts from horizontal browning to vertical blackening. To verify that the browning effect of the inner core sheets meets requirements, testing is typically conducted based on three criteria: micro-etch depth, acid resistance time, and browning tensile strength.<\/p>\n

B. Pre-preg (PP)<\/h3>\n
    \n
  1. Composition<\/strong>: Commonly used PP sheets are primarily composed of epoxy resin and glass fiber.<\/li>\n
  2. Key Physical Properties<\/strong>\uff1a\n
      \n
    • Resin Content RC%: The proportion of epoxy resin; its content can be determined using the test method specified in IPC-TM-650 2.3.16.<\/li>\n
    • Gel Time (GT): The time required for curing from the B-stage to the fully cured C-stage at 170\u00b0C, as determined in accordance with the test method specified in IPC-TM-650 2.3.18.<\/li>\n
    • Volatile Matter V.C%: Measures the residual solvent content in PP sheets after the impregnation process; testing may be conducted in accordance with the method specified in IPC-TM-650 2.3.19.<\/li>\n<\/ul>\n<\/li>\n
    • Features<\/strong>\uff1a\n
        \n
      • As a dielectric between the core board and the copper foil.<\/li>\n
      • Impedance Control: Ensure the appropriate insulation thickness.<\/li>\n<\/ul>\n<\/li>\n
      • Specifications<\/strong>: The main PP sheet specifications currently in use include 106, 1080, 3313, 2116, 1506, and 7628. The laminated thickness varies depending on the PP sheet specification and the rubber content within sheets of the same specification.<\/li>\n
      • Storage Conditions<\/strong>: Can be stored for 180 days at a humidity of \u226450%RH and a temperature of \u22645\u00b0C; can be stored for 90 days at 20\u00b12\u00b0C.<\/li>\n<\/ol>\n

        Laminating Equipment<\/h2>\n

        1. Types of Hot Presses<\/h3>\n

        Depending on the heating method, there are currently two main types:<\/p>\n

          \n
        1. Electric heating: This was an early method of heating, but it is rarely used today due to its unstable temperature.<\/li>\n
        2. Hot oil heating: The heat transfer oil is heated by a boiler, and the heat is then transferred from the oil to the press. This method provides a more stable heat supply and is easier to control; currently, the vast majority of presses use this heating method.<\/li>\n<\/ol>\n

          2. Top-down pressure method<\/h3>\n

          The vast majority of presses use hydraulic pressure, which is transmitted through a cylindrical cylinder moving from the bottom upward.<\/p>\n

          3. Key Control Points<\/h3>\n
            \n
          • Vacuum<\/strong>: Before the material enters the press and before the pressing process begins, perform a vacuum extraction to prevent air bubbles from forming during the pressing process.<\/li>\n
          • Time<\/strong>: The temperature, pressure gradient, and holding time at each stage primarily affect the heating rate and curing time.<\/li>\n
          • Pressure<\/strong>: The pressure applied to the production plates at each stage primarily affects resin flow and stress relief.<\/li>\n
          • Temperature<\/strong>: The temperature of the hot plates in the press at each stage primarily affects the actual temperature of the produced panels.<\/li>\n<\/ul>\n

            4. Key Quality Considerations After Laminating<\/h2>\n
              \n
            1. Reliability of Production Boards<\/strong>\uff1a\n
                \n
              • Thermal Stress: Measures the heat resistance of production boards; the test method typically involves thermal shock (288 \u00b1 5\u00b0C, 3 tin-dipping cycles, 10 seconds each).<\/li>\n
              • TG: To determine whether the PP on the production board has fully cured, the test method is IPC-TM-650 2.4.25 DSC.<\/li>\n
              • Peel Strength: Measures the bond strength between the copper foil and the PP substrate in the finished circuit board; the test method is IPC-TM-650 2.4.8.<\/li>\n<\/ul>\n<\/li>\n
              • Thickness<\/strong>\uff1a\n
                  \n
                • Measure the thickness of each dielectric layer using cross-sections.<\/li>\n
                • Use a thickness gauge to measure the thickness at the edges and in the center of the production panels, typically at 5 or 9 points.<\/li>\n<\/ul>\n<\/li>\n
                • Appearance<\/strong>: Ensure there are no dents, indentations, wrinkled copper foil, white edges, white corners, or other defects.<\/li>\n<\/ol>\n

                  Defects that occur during the lamination process are usually not detected until after the outer layer has been etched (particularly resin voids, white edges, and white corners). By that time, more than 3\u20135 days have already passed since the production boards entered the lamination process, making it difficult to trace the cause of the defects.<\/p>\n

                  Based on past experience, abnormalities are typically caused by issues with process operations, materials, or equipment. Therefore, during daily operations, it is essential to strictly adhere to standards; equipment inspections and tests must be completed on schedule; and if an abnormality occurs, operations must be stopped immediately to resolve the issue\u2014under no circumstances should operations continue under risky conditions.<\/p>\n

                  If you have any questions or concerns regarding the multilayer PCB manufacturing process, please feel free to contact the professional team at Jingpeng Electronics at any time; we will be happy to assist you.<\/p>\n

                  \n

                  Frequently Asked Questions<\/h2>\n

                  1. What is a multilayer printed circuit board?<\/h3>\n

                  A multilayer printed circuit board is an electronic circuit board with a multi-layer stacked structure used to connect and support electronic components.<\/p>\n

                  2. Why does the inner core panel need to undergo a browning (or blackening) treatment?<\/h3>\n

                  The browning (blackening) treatment increases the surface roughness of the inner copper foil to enhance the bond between the PP sheet and the copper surface, ensuring good lamination results.<\/p>\n

                  3. What is a thermal shock test?<\/h3>\n

                  Thermal shock testing is a method used to evaluate the ability of materials or products to withstand extreme temperature conditions. In the multilayer board manufacturing process, it is used to measure the heat resistance of the boards produced.<\/p>\n

                  4. Why is vacuum extraction necessary?<\/h3>\n

                  Vacuum extraction is used before pressing to remove air, prevent the formation of bubbles during the pressing process, and ensure the quality of the pressed product.<\/p>\n

                  5. What are some common quality issues in the lamination process?<\/h3>\n

                  Common quality issues include thermal stress, incomplete PP curing, insufficient adhesion between the copper foil and the PP, uneven thickness, and cosmetic defects. These issues can lead to process abnormalities and PCB quality problems.<\/p>","protected":false},"excerpt":{"rendered":"

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