Allegro PCB Miniaturization Option

High Dense Interconnect (HDI): The continuing miniaturization also requires a denser setting of vias. HDI boards enables a very dense placing of footprints which may even overlap if necessary. The curcuit board manufacturer determines the boundaries. In the Allegro PCB Miniaturization Option also the space-saving stacking of vias is supported. Considering the stage of production of the layer structure it is possible to propose space-saving combinations of blind and buried vias to switch from one layer to the other. HDI rules are increasingly used in impedance controlled designs with fast working times.    



Miniaturization by Embedded Components

Embedded or also buried components have severel advantages. Though the curcuit boards are created in divers single steps, components placed on it and that followed the inside fitted layer groups are injected for the final pcb. Usual pcb layout software is not able to place components in the inner layers and test all necessary design rules for embedded components. In the Allegro Miniaturization Option all important design rules for this technologie are integrated. So components can not only be fitted on the previous outer solder sides. The placement is effected on the inner layers which were released for this component assembly prior to this. It is also defined if the inner layer is fitted from above or below, according to the manufacturing steps. The distances to the copper elements of adjoining layers are tested and in case of undercut a design fault is indicated. Also automatically generated during the placement of a component are safety zones and prohibited zones as well as cavity, around its dimensions. 



Which components are suited for today's manufacturing process to be integrated in circuit boards? For passive components large ranges of values can be used (Resistors of 10 ohms up to 10 Mohm and condensators with capacities of up to 100 AF). In the passive configurations are possible 0402 and 0201 with a component height of 100 microns to 300 μ. For acitve components such as diodes and ICs, ultrathin chips without housing (bare-die) are processed with a height of 100µm til 150µm and up to a number of 50 connections.

Design Rules for Embedded Components

In the setup for embedded components the very strongly varYIng parameters can be registered for the respective pcb manufacturer and his optimized assembling process. If a component is placed on An inner layer the values are evaluated. In the layer structure for example is defined if the component on the inner layer 6 will be solded aligned upwards or downwards. Whether the component height is bigger than the isolating material between the layers, and forces through the adjoining layer, then this behaviour (protruding) must be permitted. Otherwise there is an error message already during placement. If a forcing is permitted, it is necessery to create prohibited zones on the adjoining layer, for there located signals, so that a cavity can be made. In the PCB Editor these keep-out zones are generated automatically during the placement. With the placement mechanical cutouts (cavities) /layerd-based milling in the isolating material around the component are generated, which are empty at the time of placement, but while the manufacturing process are refilled with melted resin and enclose the component in the mounted state. 

In addition to the mechanical cavity in the layer also the prohibited zones according to the setup are generated around the component. There are differences for the distances to the next routing (route keep out), the next via (via keep out) and minimum distances to the following embedded component. If there are placed two embedded components in parallel or one upon the other, then the cavity geometry has to be adjusted, that the resin can flow into the complete cavity of both parts. For this it may be permitted, to use for two components a large common cavity or each component gets his own cavity, and leads with a minimum width seperate the two cavities. Different manufacturers allow different sizes.

There is also made a difference between direct and indirect contact of the components on inner layers. The direct contact is similar to the reflow soldering and the components are directely connected onto PADs. For the inderect contact a defined via with its respective hight is chosen and implemented as buried via between the PAD and the connection point of the component.


Embedded Components for flex-rigid printed boards

When connectors or cable feeds compress too much the geometric solution and a higher reliability is required, then flexible or flex-rigid circuit boards are used. In this case the fitted ranges can be bent in the way that they are placed one upon the other. For the production of a flex-rigid board a continous flexible foil, equipped with conductor tracks is taken as basis. In the later rigid areas the pcb will be pressed as conventionally with pcb material. Given that the layer structure with severel rigid areas can be different it is necessary to place components also onto the other layers in addition to Top and Bottom. It is also possible to place components directely on the flexible foil for which special design rules are relevant. Often sensors are fitted on flexible conductor foils, because the feed lines offer not only higher reliability in mechanic bat also have a defined length and the sensor signals do not falsify via different cable lenghts with varying electrical values the sensitive sensor signals. The required rules for flex-rigid pcb can be adjusted in the Allegro PCB Miniaturization Option and the software checks online for violations of design rules.



Component placement on rigid-flex PCB



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