Single-chip integrated circuit module

Details Single-chip integrated circuit module Single-chip integrated circuit module

2000-04-03

2002-06-11

Jackson, Stephen W. (Department: 2836)

Electricity: electrical systems and devices

Safety and protection of systems and devices

With specific circuit breaker or control structure

C361S118000, C361S688000

Reexamination Certificate

active

06404611

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to the development and manufacture of one of the most important component of the microelectronics equipment, namely to the single-chip integrated circuit (IC) module made in the form of a packaged IC.
BACKGROUND OF THE INVENTION
A problem of effective protection of modern IC chips from external influences is the most principal in providing a quality and reliability of the electronic equipment at manufacture, test and usage stages. This problem is solved by means of individual packaging the IC chip in a special capsule made in the form either of a monolithic package, as a rule from a plastic, or a package from various materials with a cavity for the chip. In so doing, chip contact pads are coupled electrically with output terminals built in the package, by means of which an IC mounting on a circuit board is carried out. Thus, besides protecting the chip, the package with output terminals plays the role of a binding element for integrating the IC chip into the unified electrical circuit of the equipment.
Besides protecting and mounting functions, the package has to perform also thermo-dispersing element functions, since when operating as a part of the equipment the IC chips evolve a significant heat output. Moreover, at clock frequencies of more than 50 MHz for multi-terminal IC's a problem of parasitic impedances becomes actual, arising because of connecting to IC chip contact pads the package elements and topological circuit board elements having their own individual and mutual capacities and inductances unyielding to effective account and compensation and reducing at high frequencies the signal-to-noise ratio in signal exchange lines between chips being a part of a unified equipment assembly.
A growth of the integration degree and IC chip sizes, growth of the clock frequency, increase of a heat output and a contact pad number toughen requirements to characteristics of packages as means for packaging IC chips for their integration in an equipment. At present, once the IC integration degree has reached 10 and more millions transistors, the clock frequencies have come close to the borderline of 1 GHz, the chip sizes have become more than one cm
2
, the heat output has come to tens of W, and the number of contacts exceeds 400, now a significance of package elements for IC chips has become a governing factor in a usage of IC's, and a degree of conservation of initial characteristics of an IC chip, built in it during its development and manufacture, depends on a sophistication of a single-chip module structure.
Any structure of the capsule (package) of the single-chip IC module decreases, in one extent or another, main initial chip parameters. For example, it can be listed the following estimations of decrease (deterioration) of the initial chip characteristics for the IC chip of the Pentium 266 MMX class in the Socket 7 standard package:
in frequency characteristics—4 (i.e., the clock frequency of the chip is 266 MHz, and maximum clock frequencies outside the package on the circuit board are 66 MHz);
in dimension characteristics—50 (i.e., the chip area is about 1 cm
2
, and the area occupied by the single-chip module in the Socket 7 standard ceramic package on the circuit board is 50 times greater);
in weight characteristics—100 (i.e., the chip weight is 0.5 g, and the single-chip module on the basis of the Socket 7 standard package weights 50 g);
in price characteristics—10 (i.e., the estimation of the chip price at manufacturer is 20 $, and the seller's price of the IC in the Socket 7 ceramic package is 200 $, and taking in account all consequences of the chip characteristic weakening because of packaging, the estimation of the price coefficient can reach 100 and more).
In recent years the most wide usage for complex chips having a great integration degree is gained by cermet packages in the BGA (Ball Grid Array) standard with a system of output terminals in the form of balls on the package surface, and in the PGA (Pin Grid Array) standard with a system of output terminals in the form of pins. In so doing, the number of output terminals can ranges up to 400 and more.
BGA packages are mounted on the circuit board by means of soldering ball terminals to an array of mating contact pads on the board.
PGA packages are mounted on the circuit board using a socket with zero force, since at great number of terminals, the forces for pushing in and pulling out a great number of terminals in a common socket become comparable with forces for destroying elements of the PGA package and socket itself.
A single-chip IC module is known which is made using the PGA package, including a header from ceramic in the form of a square plate with a square hollow in the plate center intended for placing the IC chip, a hollow bottom being metallized in a chip attachment place; output terminals of a pin type disposed around the header periphery from a side of the square hollow in several rows within a predetermined coordinate grid; cross-arms with contact pads placed uniformly around the square hollow edge periphery and intended for welding conductors which one ends are welded to contact pads of the IC chip fixed in hollow bottom, and other ends are welded to contact pads of the cross-arm; a system of conductors connecting contact pads of the cross-arm with the pin type output terminals, which system is made in the form of multilayer circuit structure formed during the process of manufacturing the header and placed within the header, conductors of said structure being made from a conductive paste by screen print techniques; a cover which, after soldering, forms, along with the header, a closed volume protecting the chip and cross-arm with the wired conductors welded to the contact pads of the chip and cross-arm from an external influence. At great number of terminals, the hollow edges are formed as several benches/floors on which the contact pads of the cross-arm are placed.
Substantially, the header is a ceramic multilayer board for one IC chip, the chip contact pads being connected to the pin type output terminals built in the header via the wire couple with the cross-arm contact pads (E. H.
a
HOB
.




H
a


, Moc
KB
a:
, 1990. C.37-38,
,15a,6) (E. N. Panov, <<Pecularities of assembling the application-specific high-intergration IC's on base array master chips>> Moscrow, <<High School>> Publishing House, 1990, pp.37-38, FIG. 15
a,b
—Russian).
This structure of the single-chip module ensures a good protection, including the vacuum-tightness, of the inner closed volume with the chip from external influences and also has satisfactory thermo-mechanical characteristics (a resistance to raised temperatures and thermal cycles, a high mechanical strength) and a heat conductivity of ceramic details, which allows to perform a packaging of great chips with a high heat release.
With the indicated advantages, in the process of employing packages of such structure the following disadvantages take place: relatively great weight and sizes; a raised coefficient of thermal expansion, which leads, at great package dimensions, to difficulties in matching thermo-mechanical parameters of elements of the package and circuit board; high complexity and labor content in manufacturing the package, and also in mounting the chip and welding contact pads onto the cross-arm; a usage of a defect-creating process of welding when mounting, which reduces a yield percentage of fit items when assembling and reliability in use, as a result increasing the labor content and cost price of manufacturing the IC module as a whole.
Moreover, a usage of a non-group welding process for multi-terminal chips brings to increasing the assembling time and increasing a probability of assembling machine malfunction, which influences negatively onto the assembly productivity and yield percentage of fit items, and consequently leads to raising the cost price of the single-chip module manufacture.
Moreover, the package structure is characterized by a com

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