DE19744892A1 - Sequential fixing of layers during manufacture of multilayer circuit boards - Google Patents

Abstract

The process comprises laying each layer (1) between two other layers with one or more melting layers (2). After alignment (5) the layers are secured against horizontal displacement by applying heat using an induction loop (4) to melt the melting layers and connect the layers.

Description

Sequential fixation of the layers by inductive heating

In the "prior art" process, the pre-punched layers and melt layers are used the multilayer (ML) circuit boards when folding them together with locating pins on lay-up plates fixed. Because the fixing pins of the laying plates and the punch holes on individual layers If there is tolerance, the layers on top of each other have a horizontal offset to each other. This offset is due to the design and can be proportional to the number of layers of ML PCBs overgrow. By further refining conductor structures and Bores, the density of the conductor tracks and the bores on the layers increases continuously.

The new method now makes it possible for a robot to lay the layers can be used with optical alignment. The problems of the old method with regard to the alignment and positioning of the layers can thus be eliminated.

The new method is the sequential fixation of the aligned and layers of ML packages stacked on top of one another without pins, these individual layers sequentially fixed at each point after hanging up. The individual fixing points on the layers by inductive heating using inductors (Induction loops) heated. By transferring heat from the layer to the one below the affected areas are melted and an adhesive effect achieved. The layers are then fixed together.

The heating can take place immediately or by means of cylinder stamps. Here, the Inductors fed by high frequency (HF) inverters, so that the inductors to the generate an electromagnetic field. With immediate warming the corresponding copper spots on the layers are heated directly by inductors. At The heating by means of cylinder stamps is carried out by the corresponding copper points Heat transfer of the stamp warmed. This procedure enables pinless fixation of individual layers for pressing an ML package.  

Conventional fixation of the ML packages before pressing

In the conventional fixing processes of the ML packages, the layers are punched out first. The punched layers are placed on fixing pins during the formation of the ML package and then pressed according to FIG. 1. The locating pins ( 5 ) on the laying plates ( 4 ) and the punched holes ( 3 ) in the layers ( 1 ) (and in the fusing layers 2 ) are subject to dimensional play (tolerance), which is why the layers lie on the laying plates ( 6 ) with a horizontal offset to each other. This horizontal offset causes alignment problems of the bore pads lying one on top of the other and thus through-contact problems during electroplating according to FIG. 2 of the bore walls. Due to the further development of printed circuit board technology, the conductor tracks and the holes on the individual layers are becoming denser, which means that the dimensional play in conventional methods for fixing the layers is no longer acceptable. For these reasons, a precise fixation and positioning of the layers is necessary when forming the ML package of the further developed ML circuit boards.

Referring to FIG. 2, the horizontal offset of superposed layers (1, 2) demonstrated in the ML package. This offset is clearly visible in the case of the bore pads ( 3 ) because the distance between the bore center line ( 4 ) and the individual bore pads is different. The reason for this offset is the dimension play a between the punch holes ( 5 ) in the layers and the fixing pins ( 6 ) on the laying plate ( 7 ).

New process

Referring to FIG. 3 shows the principle of induction heating is demonstrated. The layers ( 1 ) and melt layers ( 2 ) are first aligned ( 5 ), then placed on top of each other ( 6 ). Subsequently, these layers are individually fixed at defined points by induction heating ( 7 ). This process repeats itself until the ML package is completely built.

In the case of inductive heating, inductors ( 4 ) are used to name inductors which heat the fixing points on the layers. This inductive heating can take place either by means of a stamp ( 3 ) or by direct heating.

• a) When heating by means of stamping, an electric field is generated in the stamp by inductors as shown in FIG. 3 ( 3 , 4 ). As a result of this electrical field, eddy currents are produced in the massive and / or profiled stamps "which then heat the stamps to a defined temperature. The stamps placed on the layers transfer the heat to the layer, which then transfers the heat to the melt layer melt and glue the corresponding melt layer positions. This process then fixes the layers sequentially when laying the ML package.
• b) In the case of direct heating, as shown in FIG. 4, the inductors ( 3 ) are positioned over the fixing points on the layers ( 1 ). The fixing points consist of copper pads ( 5 ) which are insulated against the remaining conductor tracks and copper surfaces. In this process, the electric field is built up directly in the copper pads by induction, thereby generating eddy currents in the copper pads. This process heats the copper pads to a defined temperature. The heat is then passed on from the copper pads to the melt layer ( 2 ), the melt layer melts and glues at the affected areas. As a result, the layers are connected and fixed sequentially ( 4 ).

In both variants of inductive heating, an electric field is created by induction built up on the affected medium (stamp, copper pad), whereby this medium by Eddy currents is heated very quickly. Through the heat transfer from the layers to the The heat-affected melt layers are melted and melted activated.

With this procedure, the individual layers of the ML packages, with an unlimited number on layers, after the more precise alignment (e.g. fully automatic precise alignment) pinless fixed. Depending on the thickness of the layers and number of ML packages, the number of Fixation points and the duration of heating to achieve better efficiency vary.  

General explanations

The layers generally consist of a composite of non-conductive inner material, as well as full-area or structured electrically conductive materials. The electric conductive materials can be either one-sided or two-sided on the inner material be upset.

The enamel layers consist of a composite fabric and are impregnated with a resin. The Melt layers are used for electrical separation of the layers as well as for mechanical Connection of the layers used. The resin of the melt layers is obtained by applying heat brought into a viscous state, after a defined time and temperature and below When exposed to pressure (press), the individual layers become mechanically firm into a package connected. If the resin is heated above a defined breakpoint (time "temperature), and after it has cooled down, it can no longer melt on a second supply of heat become (irreversible process). However, if the temperature of the heat is very high, the resin will decompose.

In sequential pre-fixation, the fixation points are warmed up simultaneously, so that a uneven expansion of the layer is prevented. Depending on the need, the Number of fixation points selected. The heating temperature as well The amount of heat depends on the thickness and the type of base material. For faster and stronger bonding of the layers can change the stamp shape and heating performance other be determined.  

Explanation of the drawings

The drawings shown are not to be understood as final embodiments, rather, they have an exemplary character for the description of the process.

In a highly simplified schematic representation, they show:

Fig. 1 Conventional fixation of the pre-punched layers on carrier plates using fixing pins to the ML package.

1 layer
2 melt layer
3 punch holes
4 laying plate
5 fixing pin
6 Fixing the layers on laying plates using fixing pins

Fig. 2 Horizontal offset of the layers in the ML package, fixation with the conventional method.

1 melt layer
2 location
3 hole pads
4 hole
5 punch hole
6 fixing pin
7 laying plate

Fig. 3 shows a first variant of the sequential fixation of the layers to the ML package, with the new method.

1 layer
2 melt layer
3 stamps (solid / profiled pins)
4 inductor (induction loop)
5 Align the layers to be fixed
6 Laying the layers together
7 Fix the individual layers

Fig. 4 shows a second variant of the sequential fixation of the layers to the ML package, with the new method.

1 layer
2 melt layer
3 inductor (induction loop)
4 Aligned and folded layers for fixing
5 copper pad

Fig. 5 Detailed recording of the new method according to the first variant using an inductor and stamp.

1 inductor
2 stamps
3 location
4 melt layer
5 Melted melting point

Fig. 6 Detailed recording of the new method according to the second variant by means of an inductor and without a stamp.

1 inductor
2 location
3 melt layer
4 Melted melting point
5 copper pad

Claims (8)

1. Claims are made on a method for sequential fixing of the individual layers of the multilayer printed circuit boards. Here, the individual layers are placed sequentially with one and / or more melt layers between two layers. After aligning and placing the individual layers, they are fixed against horizontal displacement simultaneously and / or sequentially at defined and / or variable fixing points by applying heat. The heat is generated by inductive heating using inductors (induction loops). Due to the heat transfer to the melt layers, the heat-affected areas are melted and / or completely melted. Through this process, layers are connected to one another and thus secured against displacement and / or until subsequent fixing and / or until the stack is pressed.
In this variant of the new method, the individual layers ( 3 ) are fixed according to FIG. 5 after alignment at defined and / or variable point-shaped fixing points, by heat transfer to the melt layer ( 4 ) using a stamp ( 2 ). These stamps are heated to the required temperature by inductors ( 1 ) and placed on the layers. Subsequently, the required amount of heat is transferred to the melt layers, these melt layer points ( 5 ) melting. This process connects the individual layers and fixes them against displacement. 2. In the second variant of the new method, according to FIG. 6, the individual layers ( 2 ) are heated directly by means of inductors ( 1 ) without the use of stamps. The inductors are located above the fixing points and induce an electric field in the copper pads (copper points) ( 5 ). The copper surfaces of the fixing points are heated by the eddy currents and transfer the required amount of heat to the melt layers ( 3 ). As with the first variant, the layers are glued and fixed by melting the melt layers ( 4 ). 3. Manufacturing method according to claim 1, but the fixing points are on both Sides of the layer stack (n and n + 1). 4. Manufacturing method according to claim 2, but the fixing points are on both Sides of the layer stack (n and n + 1). 5. Manufacturing method according to claim 2, however, the fixing points against the rest Copper surfaces not insulated. 6. Manufacturing method according to claim 1 and 3, but the stamps are not directly on the Layers lowered. The heat transfer from the stamps to the layers is controlled by means of a gaseous medium performed.   7. Manufacturing method according to claims: claim 1, claim 3, claim 6, but are Fixation points isolated from the remaining copper surfaces. 8. Manufacturing method according to claims: claim 1, claim 3, claim 6, claim 7, however, the stamps are heated by means of heat radiation.