In the lamination process of PCB manufacturing, pressure control is a key factor affecting the bonding quality, electrical performance and mechanical strength of multi-layer boards. The following are the core points and specific measures of pressure control:
First, the core requirements for pressure control
Pressure magnitude
Basic requirements: The pressure must be sufficient to ensure a tight bond between the materials, but excessive pressure should be avoided to prevent deformation of the sheet or excessive extrusion of the resin.
Parameter example: Taking a semi-cured sheet with a Tg value of 135℃ as an example, the initial pressure is approximately 100Pa. After maintaining for 20 minutes, it is gradually increased to 225Pa to ensure that the resin flows fully and fills the interlayer voids.
Pressure uniformity
Uniform distribution: The pressure should be evenly applied to all areas of the sheet to prevent poor lamination (such as interlayer separation or warping) due to insufficient or excessive local pressure.
Equipment requirements: High-precision pressing machines should be adopted to ensure the balance of pressure distribution.
Pressure and temperature work in coordination
Collaborative control: Pressure and temperature need to be regulated in coordination. For instance, the heating rate should be controlled at 24℃ per minute to prevent abnormal resin fluidity caused by excessive heating (such as poor wettability or weak adhesion).
Second, specific measures for pressure control
Apply pressure in stages
Pre-lamination stage: Preliminary lamination is carried out under low temperature and low pressure to ensure the initial bonding of interlayer materials and prevent the entry of air and impurities.
Formal lamination stage: Under high temperature and high pressure, the resin fully flows and cures, forming a firm bonding layer.
Material compatibility
Brand consistency: The inner core board, semi-cured sheet and copper foil should be of the same brand to ensure that the expansion coefficient and shrinkage rate of the materials match and reduce the stress difference during the lamination process.
Characteristics of semi-cured sheet: Adjust the pressure parameters according to the Tg value, resin content (RC%) and fluidity (RF%) of the semi-cured sheet to ensure the resin filling effect.
Environmental and process control
Environmental control: The humidity and cleanliness during the lamination process must be strictly controlled to prevent the resin from absorbing water or being contaminated on the surface, which may affect the lamination quality.
Process parameter optimization: Precisely adjust the pressure, temperature and time based on the number of layers, thickness and material properties of the sheet to ensure the fluidity and curing effect of the resin.
Third, the consequences of improper pressure control
Insufficient pressure
Poor interlayer adhesion: The resin does not fully fill the interlayer voids, resulting in interlayer separation or unreliable electrical connections.
Decreased mechanical strength: The sheet is prone to breakage or deformation during subsequent processing or use.
Excessive pressure
Sheet deformation: Excessive pressure may cause the sheet to warp or have uneven thickness.
Resin extrusion: Excessive resin extrusion leads to a lack of glue in the laminate, affecting its mechanical and electrical properties.
Uneven pressure
Poor local lamination: Some areas of the board show loose adhesion or interlayer slippage, resulting in poor circuit connection.
Signal transmission issue: Uneven lamination may affect the geometric structure and characteristic impedance of the signal transmission line, leading to signal attenuation or distortion.
