An Overview of The Problem of Heat Removal from LSI Crystals

long with an increase in the number of VLSI pins, the power released on the crystal increases to tens of W, which, naturally, is associated with the problem of heat removal from the crystal.

Due to the standard design (PC), it is impossible to carry out heat removal directly to the equipment case, as a result of which forced air convection is used, and personal micro-fans are installed for large crystals.

In household equipment, this can still be tolerated, however, for special equipment with high-reliability requirements and harsh operating conditions, this cannot be allowed.

How to Solve a Problem?

In 1979 Charles Lassen was the first to criticize the PP.

He made an article “Requires a new interconnection technology”, in which he examined in detail the state of affairs and further prospects for solving the problem.

Later, this direction was developed in the works of Jerry Lyman, who foresaw the transformation of PCBs into large hybrid integrated circuits (BGIS).

Undoubtedly, the proposal, which was put forward in 1968 by the Americans Marley and Trolsen, on the use of polymide film with the subsequent creation of flexible hybrid integrated circuits (GIS) on its basis, was successful in confronting PP and BGIS.

Nevertheless, the transfer of the through-hole principle from the PCB technology entailed a number of technical problems, which became the reason for the high manufacturing complexity.

Thanks to the vast experience we have accumulated in this area, a fundamentally new process for the manufacture of rigid and flexible PP and BGIS was developed, eliminating the noted disadvantages.

This method excluded the use of foil-clad fiberglass, through holes from the structure, and chemical processes such as etching of a thick copper layer, metallization of through-holes with palladium and copper, and etching of holes in a flexible polyamide film were excluded from the technological cycle.

All of the above allows you to create an environmentally friendly production of PP and BGIS without the need to build treatment facilities.

According to the new technology, foil-clad fiberglass is replaced by a film of any polymer, metalized in a vacuum with a thin (2-3 microns) layer of copper.

The formation of electrical transitions occurs mechanically on CNC machines.

This method of forming an electrical junction expands the list of materials used since no polymer lends itself to chemical etching except polyimide.

The resulting double-sided flexible circuit can be pressed onto any rigid base made of plastic, cardboard, composite material, metal.

I would like to note that the arrangement of electrical radioelements (ERE) on one side in the new design of the boards made their group installation very convenient, in addition, facilitated the continuity of the circuits.

In addition, you can use the other side of the base to position another flex board. In this case, there is no need for a backplane for switching through the add connectors, because the connection can be made with one or more loops.

BGIS is a basic element for building a multilayer structure. The vertical electrical connection between different boards occurs during the monolithization of the package when it is pressed to the base.

With a high density of conductors in each electrical layer, the number of layers of a finished multilayer PCB is significantly less than a typical multilayer PCB.

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