Flexible printed circuit (FPC) with reinforced bonding pad at top and thermal printing head
By adding copper foil reinforcement pads on the top of the FPC flexible circuit board, the pressure of the hot press head is concentrated on the lower gold finger of the FPC and the substrate PAD, the problem of poor reliability of the FPC and ceramic substrate is solved, and the reliability of ACF bonding and the performance of the product after aging experiment is improved.
Patent Information
- Application Number
- CN202420807286.3
- Authority / Receiving Office
- CN · China
- Patent Type
- Utility models(China)
- Current Assignee / Owner
- Filing Date
- 2024-04-18
- Publication Date
- 2025-03-21
- Estimated Expiration
- 2034-04-18
AI Technical Summary
During the ACF hot pressing process between the FPC flexible circuit board and the ceramic substrate, uneven pressure leads to poor bond reliability. After the accelerated aging experiment, the conductive particles of the ACF layer are prone to free, resulting in large conduction impedance and poor reliability.
Reinforcement pads are added on the top of the FPC flexible circuit board, and copper foil material is used, with the area consistent with the FPC gold finger receiving area, which concentrates the pressure of the hot press head on the effective PAD of the substrate to reduce the stress of the film between the FPC gold fingers.
By concentrating pressure on the lower gold finger of the FPC and the substrate PAD, the reliability of ACF bonding is improved, the rebound stress is reduced, and the product maintains good performance under high temperature and high humidity conditions.
Smart Images
Figure CN222655403U_ABST
Abstract
Description
Technical field:
[0001] The utility model relates to the technical field of thermal print head manufacturing, and specifically to an FPC and a thermal print head with a reinforcing pad added to the top, which can effectively improve the reliability of the combination of an FPC flexible circuit board and a substrate PAD area, thereby improving the product quality of the thermal print head. Background technology:
[0002] AFC process, or Anisotropic Conductive Film process, is a connection technology used in the field of electronic packaging. It combines the functions of conductivity and bonding to achieve electrical and mechanical connections. ACF materials are usually composed of conductive particles and adhesives. These conductive particles can be metal particles or small plastic balls with metal coating on the surface. They are dispersed in the resin material to form a film. During the ACF hot pressing process, the ACF material is bonded to the connection object (such as a printed circuit board, display device, chip, etc.) by hot pressing to form an electrical and mechanical connection. Figure 1 As shown, in the manufacturing process of the thermal print head, the FPC flexible circuit board needs to be connected to the metal welding area on the ceramic substrate, that is, the FPC integrated circuit needs to be bonded to the ceramic substrate through a hot pressing device to achieve the connection between the FPC and the electronic components on the ceramic substrate.
[0003] When performing ACF hot pressing on FPC and ceramic substrate, in order to ensure the flatness of the two components, a buffer material layer is usually added under the hot pressing head. On the one hand, the buffer material layer can make the force applied to the product during pressing more evenly, and on the other hand, it can absorb the impact force generated by the ACF hot pressing equipment during the hot pressing process by deformation. When pressing the product, not only the position where we want to conduct, that is, the gold finger at the bottom of the FPC and the effective PAD of the substrate, will be subjected to the applied pressure, but also the deformation of the buffer material during pressing will cause the membrane between each FPC gold finger in the invalid area to be subjected to a large force, resulting in a certain degree of depression, as shown in the attached figure. Figure 5 After the product has been subjected to an accelerated aging test, namely the PCT (high temperature cooking) test, the experimental conditions are: 121°C, 0.2mpa, 100% humidity, 24h, the Space area is very prone to ACF rebound, as shown in the attached Figure 6 As shown in the figure, the conductive particles in the ACF layer are freed to the PAD area far away from the ceramic substrate, resulting in large on-resistance of the product, poor reliability, and affecting product performance and service life. Therefore, in an ideal state, during lamination, the pressure applied by the equipment can be mainly concentrated on the gold fingers at the bottom of the FPC and the effective PAD of the substrate, reducing the stress on the membrane between each FPC gold finger and reducing the rebound stress. Summary of the invention:
[0004] The utility model aims at the shortcomings and deficiencies in the prior art and proposes an FPC structure which can improve the reliability of ACF bonding and at the same time can maintain the good performance of the product after an accelerated aging test (PCT) by adding a reinforcing pad to the top of the FPC and a thermal print head.
[0005] The utility model achieves this through the following measures:
[0006] An FPC with a reinforcing pad added to the top is provided with a flexible covering film, a conductive circuit layer is provided on the lower side of the flexible covering film, and an FPC gold finger for connecting to a metal welding area on a substrate is provided on the conductive circuit layer. The invention is characterized in that a reinforcing pad is provided on the upper surface of the flexible covering film, the reinforcing pad corresponds to the setting area of the FPC gold finger on the lower side of the flexible covering film, and the area of the reinforcing pad is consistent with the acceptance area of the FPC gold finger.
[0007] The reinforcing pad of the utility model adopts copper foil, which is used to ensure that when the FPC is subjected to ACF hot pressing, the pressure of the hot pressing head is mainly applied to the top reinforcing pad, and then mainly applied to a single effective PAD pad of the substrate through the reinforcing pad, thereby reducing the stress on the flexible covering film between each FPC gold finger, thereby improving the reliability of the ACF bonding. After the accelerated aging test, namely the PCT (high temperature cooking) test, the product still maintains good performance without quality problems.
[0008] The copper foil thickness of the reinforcing pad of the utility model is between 20 and 50 um, which ensures that the force can be better concentrated on the copper foil during pressing, and can also reduce the force on the membrane between each FPC gold finger and reduce its deformation. The copper foil of the reinforcing pad is an invalid pad and is not connected to the FPC integrated circuit.
[0009] The utility model also proposes a thermal print head, which is provided with a heating substrate for the thermal print head. The heating substrate for the thermal print head includes a ceramic insulating substrate, a base glaze layer is arranged on the ceramic insulating substrate, and a heating resistor and an electrode wire are arranged on the base glaze layer. It also includes an FPC flexible circuit board. The FPC gold finger on the lower side of the FPC flexible circuit board is connected to the metal welding area on the ceramic insulating substrate through an AFC process. It is characterized in that the FPC flexible metal plate adopts the FPC with a reinforcing pad added on the top as described above.
[0010] Compared with the existing structure, the structure of the utility model product makes the force applied during product pressing mainly concentrated on the gold fingers at the bottom of the FPC and the substrate PAD through the top solder pad, reducing the force on the membrane between each FPC gold finger and improving the reliability of ACF bonding. Description of the drawings:
[0011] Attached Figure 1This is a schematic diagram of the ACF hot pressing process principle in the prior art.
[0012] Attached Figure 2 It is a structural diagram of an existing FPC flexible circuit board.
[0013] Attached Figure 3 It is a structural schematic diagram of the FPC flexible circuit board in the utility model.
[0014] Attached Figure 4 It is a structural schematic diagram of an embodiment of the utility model.
[0015] Attached Figure 5 It is a schematic diagram of the existing FPC flexible circuit board combined with the ceramic substrate.
[0016] Attached Figure 6 This is a schematic diagram of the combination of the existing FPC and the ceramic substrate after the accelerated aging test. Figure 7 It is a schematic diagram of the FPC of the utility model after being combined with a ceramic substrate.
[0017] Reference numerals: thermal compression head 1, buffer material layer 2, FPC flexible cover film 3, gold finger 4 at the bottom of FPC, ACF layer 5, conductive particles 6 of ACF layer, PAD area 7 of ceramic substrate, ceramic substrate 8, reinforcement pad 9. Specific implementation method:
[0018] The present invention will be further described below in conjunction with the accompanying drawings and embodiments.
[0019] As attached Figure 3 As shown, the utility model proposes a new FPC flexible circuit board. Compared with the original upper layer being a flexible covering film (PI & glue, etc.) and the lower part being a gold finger copper foil structure, in the present application, a monomer copper foil array is further provided on the upper surface of the FPC flexible covering film 3. The monomer copper foil is used to form a reinforcing pad 9. The reinforcing pad is arranged relative to the gold finger copper foil on the lower side of the FPC flexible circuit board. In this way, it can be ensured that during the pressing process of the thermal print head manufacturing, the force applied by the thermal press head 1 to the product is mainly concentrated on the gold finger 4 at the lower part of the FPC and the PAD area 7 of the ceramic substrate through the reinforcing pad 9. At the same time, the force on the invalid area of the flexible covering film Space between each FPC gold finger can be reduced, the deformation thereof can be reduced, and the bonding reliability of the ACF layer and adjacent components can be effectively improved.
[0020] Example:
[0021] As attached Figure 5 As shown in the figure, the original FPC pressed product will have a large deformation of the membrane between each FPC gold finger due to the deformation of the buffer material during the pressing process, resulting in large stress and prone to rebound.
[0022] As attached Figure 6 As shown in the figure, after the pressed product undergoes accelerated aging test (PCT), the FPC film will release stress due to the influence of temperature and humidity, and the deformation will decrease, which will cause the gold finger at the bottom of the FPC to peel off from the substrate PAD, affecting the conduction of the product and causing product failure.
[0023] As attached Figure 3 As shown, this example provides an FPC with an additional reinforcement pad on the top. Based on the original FPC structure, a layer of single copper foil corresponding to the position of the gold finger at the bottom of the FPC is added on the top of the film as a reinforcement pad.
[0024] The reinforcing pad added on the top of the utility model is made of copper foil, which has good thermal conductivity. During pressing, the heat of the hot pressing head can be better transferred to the ACF bonding area through the copper foil, so that the heating is more uniform.
[0025] As attached Figure 4 As shown, the utility model changes the top structure of the FPC, adds a reinforcing pad on the top, and the position of the single pad corresponds to the position of the copper foil of the gold finger at the bottom of the FPC. During hot pressing, the force is transmitted through the top reinforcing pad of the FPC and concentratedly to the gold finger at the bottom of the FPC and the effective PAD of the substrate, making the force more uniform. At the same time, the force on the membrane between each FPC gold finger is reduced, and its deformation is reduced to avoid rebound after high temperature and high humidity. The reliability of ACF bonding can be effectively improved. After the accelerated aging test, namely the PCT (high temperature cooking) test, the product still maintains good performance without quality problems.
[0026] Compared with the prior art, the utility model makes the force applied during product pressing mainly concentrated on the gold fingers at the bottom of the FPC and the effective PAD of the substrate, reduces the force on the membrane between each FPC gold finger, and improves the reliability of ACF combination.
Claims
1. An FPC with a reinforcing pad added to the top, provided with a flexible covering film, a conductive circuit layer is provided on the lower side of the flexible covering film, and an FPC gold finger for connecting to a metal welding area on a substrate is provided on the conductive circuit layer, characterized in that: A reinforcing pad is provided on the upper surface of the flexible covering film, and the reinforcing pad corresponds to the setting area of the FPC gold finger on the lower side of the flexible covering film, and the area of the reinforcing pad is consistent with the receiving area of the FPC gold finger.
2. The FPC with a reinforcing pad added to the top according to claim 1, characterized in that: The reinforcing pad is made of copper foil.
3. The FPC with a reinforcing pad added to the top according to claim 2, characterized in that: The copper foil thickness of the reinforcing pad is between 20 and 50 μm, and the reinforcing pad is an invalid pad and is not connected to the FPC integrated circuit.
4. A thermal print head, provided with a heating substrate for the thermal print head, the heating substrate for the thermal print head comprising a ceramic insulating substrate, a base glaze layer is arranged on the ceramic insulating substrate, a heating resistor and an electrode wire are arranged on the base glaze layer, and also comprising an FPC flexible circuit board, the FPC gold finger on the lower side of the FPC flexible circuit board is connected to the metal welding area on the ceramic insulating substrate through an AFC process, characterized in that: The FPC flexible metal plate adopts the FPC with a reinforcing pad added on the top as described in any one of claims 1-3.