2007 InduBond 130N Comparative Chemplate Materials, S.L 30/11/2007 Document revelation not allowed without Chemplate
Introduction Lamination of individual circuit layers is a process is used within the PCB industries to manufacture multilayer printed circuit boards. The process requires each layer of the multilayer assembly to be aligned to each other during the lamination cycle. The most common methods used by the electronic industry to laminate multilayer circuits: PINLAM MASSLAM The MASSLAM system has advantages when compared to the PINLAM system, which will be covered in a future document. The purpose of this document however is to explain the differences between the methods used for MASSLAM and InduBond technology. Brief description The MASSLAM system registers the different layers of the multilayer stack without the need for tooling pins during the lamination press process. There are three MASSLAM bonding systems on the market. Rivomat (Mechanical rivets) Standard bonding system (Electrical heaters) InduBond technology (Inductive Bonding)
System comparisons Rivomat system This mechanical system is probably one of the first systems developed, and is currently used in many companies in spite of its inherent limitations. The process involves the build up the multilayer stack in an accurate pin template that aligns the layers. Typically 8 holes are drilled along the longest dimension of the stack (4 holes along each edge). This process can result in copper or substrate debris being trapped inside the stack. The final operation is to insert the rivets in the holes and press them in place using a high-pressure riveting tool. The uncontrolled mechanical expansion of the metallic rivets produces internal stresses and movements, which can cause the misalignment of the individual inner layers within the stack.
Advantages: - The main advantage of this system is that the operation is relatively faster than other systems Disadvantages: - The riveting process relies on a non-uniform mechanical expansion of each rivet, which increases the risk of inaccurate alignment between the layers. - The rivet is a consumable item and different lengths are required for each panel thickness. - Longer rivets increase the risk of misalignment for high layer count panels. - The head of the rivet can protrude beyond the thickness of the stack causing damage to the tooling press plates. - The edges of the rivet heads (top and bottom) can cut and break through thin material outer layers causing them to move independently of the inner layers. - During the riveting cycle the misaligned of rivets within the feed head can block the machine, requiring maintenance.
Standard Bonding System The standard bonding system principle relies on the prepreg layers bonding to the inner layers by means of a polymerization effect. To polymerize the prepreg resin, the standard bonding system uses high temperature electric heaters similar to welders, which transfer heat from the outside to the core of the stack. The temperature of the heaters are elevated to approximately 300ºC (572ºF) Between 6 and 8 bonding points are Utilized Incorporating 2 heaters at each point. A total of 12 to 16 electrical heaters are constantly energized during production contributing to relatively high running costs. An inherent drawback with the design is the inefficient heat transfer through the substrate material to the internal layers in order to initiate polymerization of the prepreg. Due to space restraints the bonding Heads must be small as possible, typically 4mm diameter. For this reason the system needs to apply high pressure to overcome the thermal insulation properties of the laminate, glass fibre for example. The excessive bonding pressure causes deformation around the bonding area due to the poor thermal uniformity at the polymerization point. The result
At the start of the bonding cycle, the outer surfaces of the bonding points are subject to extreme temperatures of around 300ºC while the center of multilayer is relatively cold. Therefore to assure good polymerization it requires a compromise between cycle time, pressure and temperature settings. It can be difficult to achieve the optimum settings if the assembly includes thick inner layers or if the final thickness of the multilayer is in excess of 1.6mm. Two possible scenarios can result, while the core layers are at the correct temperature, the panel surfaces in touch with the heated bonding heads can be too hot and possibly burn (creating poor adhesion caused by carbonization of the epoxy resin). Conversely, the surface in contact with the heated heads is at the correct temperature while the core layers are too cool resulting in poor polymerization of the prepreg resin. The combination of high temperature and compression applied by the small surface area heated heads can create a crater/volcano effect, causing resin migration away from the bonding points. The movement of resin around each of the bonding points (6 or 8) inhibits air movement creating internal pressures, which in turn inflates the thickness of the stack.
Advantages: - The machine is simple and less costly compared to other systems. - No consumables are required, rivets for example. Disadvantages: - Uncontrolled process for different thicknesses. - The depressions at the bonding points will can cause problems in the next process: The over thickness points will not permit good pressure balance transfer to the surfaces of the stack during the press cycle. (No lineal resin flow, bending effects ) The generated over-thickness around all bonding points will damage the separated press plates on the press (very expensive). The raised areas can cause fractures at the bonded points during the press cycle, resulting in misalignment (expensive scrap, extended delivery times). The non lineal or controlled polymerization in the vicinity of the bonding points cannot guarantee uniform movement of each inner layer during the press cycle. - The system is at best unreliable for thick multilayers (more than 2mm) or back plane panels because the heat required to polymerize the centre of the stack will overheat the outer layers. - The thicker the multilayer stack the deeper the crater effect is. - The heated bonding head faces will carbonize due to the high operating temperature. The carbon can sometimes stick to the resin or fiber glass of the assemblies, which in turn can be transferred to the circuit pattern areas.
InduBond Technology The InduBond technology is a 5 years old technology developed and patented by Chemplate Materials to improve all the limitations of the previously mentioned technologies. As a reference, companies including Ruwel, Würth, Hitachi are among more than 70 companies around the world enjoying the advantages of our first generation of InduBond technology. The InduBond technology utilizes induction heated bonding heads that heat up copper etched patterns on both sides of each layer of the multilayer assembly stack. This etched copper pads heat up by means of a high frequency magnetic field that passes across the surfaces, producing high Eddy currents. Each copper pattern is penetrated by the same magnitude of magnetic field. All copper patterns on each of the layers are heated with the same energy and therefore polymerization of the resin is uniform throughout the stack. The high frequency magnetic field is produced by highly developed magnetic heads that remain cold (ambience temperature) and energise only during the bonding process.
The magnetic electrode heads having a slightly larger surface area than the copper pattern, apply only the minimum of pressure to the stack. Heat is generated using the copper of the circuit to transfer the heat to the resin of the prepregs above and below the inner layers to polymerize the bonding points.
The result of the inductive bonding point, is a flat final uniform thickness of the multilayer circuit before pressing. Uniform polymerization of resin around the inductive bonding points of the stack is achieved. The bonding points achieved by InduBond technology are elastic and flat, without over thickness. They are capable of withstanding the dilations and contractions of the hot-press cycles. Each bonded point provides maximum assurance that the linear movement of all layers in a multilayer stack will be uniform. The added benefit is minimal internal tensions that cause warping and deformations and moreover reducing the distortions and misalignments between inner layers.
Advantages: - Ergonomic design (more comfortable operator working methods compared to other machines, and improved handling around the work area to dispense the inner layers). - Compact machine (small lay out). - No thickness limit for high quality bonding. (The mechanical limit is about 30mm, the template pin height is nominally 10mm). - Flat finishing surface. No over thickness points provide: Cost savings due to increased life expectancy of separator press plates (if the stacks are flat, no press plates damage will result). Perfect pressure transferred to all layer surfaces within the stack during the press cycle. (Lineal resin flow, reduces internal stresses of the material helping to minimize bending effects). Highly stable bonding points maintain their integrity during the press cycle. (No misalignment caused by fractures or breakage). Controlled polymerization provides flat elastic bonding points that accommodate the different movements of the inner layers during press cycle without losing the registration. (reliable process and therefore less scrap). - The induction method allows 2 or 3 multilayer assemblies to be bonded simultaneously. The assemblies can be registered in the same pin tool (no prepreg sheet between each multilayer assembly). - Increased productivity available (using optional low cost pre-assembly station it is possible double the production (similar to a double drawer machine). - The InduBond heads are protected with a non-adherence material that provides a clean surface for high quality bonding. - Easy set up by touch screen for different multilayer constructions or different materials.
- Easy access to the components and low maintenance. - Safe electric power, the InduBond heads (total 3kw) are always off until the bonding cycle is initiated (standard bonding cycle from 30 to 45 seconds). Disadvantages: - The machine is a little more expensive, but easily recoverable by the money saved by increased press plate longevity. - The cycle time for a single assembly is a little longer that the rivet system. However the total production can be the same or higher if 2 or 3 assemblies are bonded at the same time, or if the machine is upgraded with the low cost pre-assembly station.