What is lamination?
Lamination is one of the major steps in manufacturing flexible circuit boards. The so-called “lamination” is a method of ensuring that the flexible substrate, copper foil and cover layer combine into a whole through lamination under certain conditions.
The lamination process mainly includes the following stages:
1. Material preparation and cleaning
Preparation of flexible substrate: A flexible substrate is usually made with polyimide or polyester. These materials possess excellent mechanical properties and heat resistance.
Preparation of copper foil: Copper foils are used for forming conductive lines. The thickness of copper foil is chosen depending on the design needs.
Surface cleaning: It is important to have thoroughly cleaned surface of a flexible substrate and copper foils to remove dust, oil, grease and other contaminants before they can be bonded together. Common cleaning methods include chemical and plasma cleaning.
Surface treatment: Copper foils also undergo a roughening process (e.g., chemical etching or mechanical roughening) in order to increase their surface area so that bonding force with bonding layer is improved.
2. Stacking assembly
Stacking order: According to design requirements, workers stack flexible substrate, adhesive layer (e.g. acrylic or epoxy), and copper foil in specific sequence.
Alignment: It makes sure there is accurate alignment between layers. Positioning holes as well as alignment marks are often used to prevent deviations during subsequent processing.
3. Hot pressing and pressurization
Laminator setting: Place the assembled stacked materials into the laminator. Set the temperature and pressure parameters of the laminator to ensure that the process requirements are met.
Hot pressing process: Hot pressing is performed under high temperature and high pressure. The time of hot pressing is set according to the material and process requirements.
Adhesive layer curing: Under heat and pressure, the adhesive layer starts softening and flowing and fills gaps between copper foil and flexible substrate. As temperature and pressure persist on acting further, the adhesive layer gradually solidifies to form a strong bond.
4. Cooling and post-processing
Cooling process: The laminate has to cool slowly down to room temperature after lamination. Rapid cooling may lead to internal stress and warpage of the material.
Removing the laminate: Remove the cooled laminate from the laminator.
Inspection and post-processing: Examine the laminate for quality assurance purposes. Inspection items include bonding strength, interlayer alignment and appearance quality. Correction and subsequent processing such as drilling, copper cladding and molding are carried out when necessary.
Notes on the lamination process
In the process of laminating flexible circuit boards, there are several key points that must be strictly controlled to guarantee the quality and dependability of end products:
Temperature control
The temperature during lamination should stay at a constant level within set range. The lamination temperature is usually about 180 °C, with ±5 °C being an acceptable deviation in order to get uniform curing of the adhesive layer. Too high temperatures probably can cause thermal damages on substrates and adhesive layers, leading to compromise on mechanical and electrical attributes of PCB, while too low temperatures might not allow for full curing of adhesive layers hence poor interlayer adhesion will occur resulting into delamination or peeling.
Pressure control
It is essential that pressure applied during lamination be distributed uniformly such that entire area under stacking experience consistent adherence. High pressure can lead to deformation of substrate whereas low pressure might produce uneven bond layer.
Pressure range: Lamination pressure ranges between 100-200 psi. For example, high pressures may result in substrate deformation especially wrinkles or deformation in thin flexible. Too low pressure will not allow the bonding layer to fully contact and cure, resulting in insufficient bonding strength and affecting the durability of the circuit board.
Lamination time
Usually, the time for lamination ranges from 30 minutes to 1 hour, but it has to be controlled exactly depending on the material features and technology requirements. If lamination time exceeds limits it may cause over-curing of materials which will worsen their flexibility and electrical properties; too short lamination time can result in incomplete curing of adhesive interface layer leading to insufficient bond strength and possible delamination during subsequent service. Therefore, to ensure that the adhesive has sufficient time to cure, it is usually necessary to monitor the curing curve of the adhesive to optimize the time setting.
Alignment technology
Using high-precision positioning holes and alignment marks to ensure accurate alignment between the layers of material. The error of alignment accuracy should be controlled at the micron level to ensure the function and performance of the circuit. The alignment error is generally controlled within ±0.1 mm in the industry, and the limit is 0.075 mm. Alignment deviation will cause circuit connection errors and affect the function and performance of the circuit board. Flex Plus can control the error within 0.075 mm to ensure the precise alignment of the circuit pattern.
FLEX PLUS can ensure the best lamination process of flexible circuit boards by strictly controlling temperature, pressure, time and alignment accuracy, and produce high-quality and reliable flexible circuit boards.
Comments