Substrates

The Materials employed tor insulating substrates of thin-film circuits are commonly glasses, ceramics and glass ceramics. Glazed alumina is most popular. Substrates are usually rectangular or square in shape. The thickness of substrates is 0.6, 1.0 and 1.6 mm.

The substrate of an 10 must have a high mechanical strength, low electrical conductivity, and good thermal conductivity. The substrate surface must be mirror-like. The degree of surface finish determines the thickness of deposited films. The process of fabrication of substrates includes several stages: blank cutting, lapping, polishing, cleaning, washing, etching, drying, and last, ion bombardment using a glow descharge. She treatment gives the desired surface finish and thus ensures a good adhesion of films to the substrate. Minute crystal defects cause appreciable changes in the properties of thin-film elements.

XI. Прочитайте текст Д и задайте 10 вопросов по содержанию текста.

Conductors and Contact Pads

Conducting films serve as interconnections, inductors, and capacitor plates.

The conductivity of a metal film depends on the film thickness. A film conducts well at a thickness of 0.1 The materials for metallized current-carrying stripes interconnecting circuit elements and contact pads must fill the following requirements.

1. High adhesion to a substrate. Contact pads are subject to thermal shocks during soldering or welding and support the leads of active elements.

2. High conductance. The circuit designer usually specifies a lower level of connection pattern conducance that ensures the adequate performance of the circuit.

3. Chemical stability. The factors affecting the quality of films are corrosion, structural changes leading to disturbances in film layers are in contact with resistive elements, capacitor plates, and dielectrics. It is, thus, essential to avoid chemical interaction of all circuit components both during the manufacture of a film microcircuit and in the operating conditions.

4. Good solderability to enable adequate circuit assembly. Contact pads serve to connect the circuit to input, output, and power supply lines and also to interconnect active elements through film stripes and jumpers.

5. The parameters of contact pads are a contact resistance, current-voltage characteristic, and noise voltage induced by contacts.

6. The materials for thin-film conductors are commonly gold and aluminum vaporized in a vacuum.

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Unit 13.

Text A. Semiconductor 1C Assembly

Text B. Typical Circuit Packages.

Text C. Assembly of Hybrid Integrated Circuits.

Grammar Revision. Infinitive.

Terminology

1. package — конструкция корпуса, корпус

2. diamond scribe — алмазный резец scribing — скрайбирование

3. dicing — резка

4. a header- кристаллодержатель, основание корпуса package header -основание корпуса

5. metal envelope -металлический корпус

hermetically sealed metal envelope — герметически спаенный корпус

6. epoxy resin coats — покрытия эпоксидной смолой

7. a metal can — металлический корпус

8. to mold — прессовать, формовать

9. lead — вывод, расположение выводов

lead pitch — размер шага расположения выводов

10. duel-inline package — корпус с выводами по длинным сторонам основания корпуса с одинаковой геометрией отгибки

11. quad-inline package — корпус с выводами по длинным сторонам основания о отгибкой в шахматном порядке

12. joint — спай

13. brazing — пайка среднеплавким припоем (с теыпературой плавления выше 500°С)

14. molten glass bonding — пайка припойным стеклом

I. Проверьте, знаете ли Вы следующие слова:

wafer (n), contain (v), separate (v), mount (v), encapsulate(v), protect (v), protection (n), influence (n), commonly (adj), welding (n), soldering (n), design (n,v), dimension (n), shape (n), however, heavy (a), light (a), ratio (n)

II. Переведите следующие словосочетания на русский язык:

after sorting out the chips; it is first necessary to mount; to connect the circuit to; plastic enclosure; ceramic and metal-ceramic package; to bond together by thermocompression; a uniform distribution of stresses; reliable sealing of the chip; planar leads; to depend on the design.

Semiconductor 1C Assembly

A set icon wafer can contain several hundred integrated circuits. Before proceeding with assembling, the wafer need be cut vertically and horizontally with a diamond scribe to separate it into individual chips. This operation is known as dicing, or scribing. After sorting out the chips, the assembly proper follows, For this, it is first necessary to mount the chip on a header, then bond or solder it to connect the circuit to the header terminals, and finally, encapsulate or package the mounted chip to protect it against mechanical and environmental influences.

Typical encapsulations for integrated circuits are hermetically-sealed metal envelopes, epoxy resin coats and other plastic enclosure, and ceramic and metal-ceramic packages. Ceramic and metal-ceramic packages are commonly meant for 1C designed to operate in adverse mechanical and environmental conditions. A metal-ceramic enclosure consists of a ceramic header (envelope bottom) and a metal can or cover bonded to the header by welding or soldering in a ceramic enclosure both the header and the can are made from a cermic material and bonded together, a plastic package has its can and bottom molded of a plastic material and bonded together by themocompression. Plastic packages are suitable for ICs intended for work in all but too arduous conditions.

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The design of a package is chosen proceeding from service conditions and requirements for equipment dimensions, type of assembly and tests of the encapsulated ICs.

Packages can be cylindrical and flat in shape, with leads running parallel or normal to the header plane. 1C packages can be classified by the overall and mounting dimensions, the number of leads, and the lead pitch (spacing between leads). The lead pitches of circuit packages are given in Table I.

Table I Type 1 Package shape Lead Lead pitch

1. Rectangular Vertical 2.5 mm

2. Rectangular Vertical 2.5 mm

3. Bound Vertical _{3Q| 36 45}o

4. Rectangular Planar 1 25 mm

All these types, except the first, are suitable for semiconductor ICs. The second type has three modifications.

1. The dual-in line package.

2. The quad-in line package.

3. The package is arranged along the perimeter and each bent in the same fashion.

The 3d type is cylindrical in shape. The round shape of the package ensures a uniform distribution of stresses in the joint, reliable sealing of the chip, and good protection of the 1C against mechanical influences. This type of package, however, suffer from some disadvantages: it can hold a chip not over 2,5 by 2.5 mm in area, has a limited number of leads, and is comparatively large in size and heavy.

The 4th type with the leads parallel to the package plane is also built in three design variants. The cans mounted on ceramic heads can be both metallic and ceramic.

Plat packs with planar leads are generally 2 or 3 mm high. The maximum power of ICs enclosed in these packs ranges from 200 mW to 1000 mW. The leads are strips 0.1 mm thick soldered to the pack walls. Depending on the design of flat packs, the assembling can be done by welding, brazing, or molten glass bonding. The main advantages of flat packs are that they are light and small, in size and exhibit a comparatively large chip area-to-pack area ratio.

Words to be learnt:

1. bo proceed — продолжить, приступить к

2. adverse conditions — неблагоприятные условия 5. arduous conditions — трудные условия

4. enclosure — оболочка, корпус

5. to intend for— предназначать для

6. to ensure — обеспечивать

7. to exhibit — показывать, проявлять

III. Переведите следующие словосочетания на английский язык:

Резать алмазным резцом по вертикали и горизонтали, резка, защитить от механических и климатических воздействий, герметический корпус, покрывать эпоксидуой смолой, керамические, металлокерамические и пластмассовые корпуса, действовать в неблагоприятных механических и климатических условиях, соединять с металлической крышкой сваркой или пайкой, условия эксплуатации, требования к габаритам аппаратуры, круглые и плоские корпуса, расположение выводов, размер шага расположения выводов, обеспечивать равномерное распределение механических напряжений в спае, выполнить сборку с помощью... , сравнительно высокое отношение площади кристалла к размером корпуса.

IV. Переведите предложения, обращая внимание на употребление инфинитива:

1) Aluminum is the most problematic material to be used tor metallization in maintaining contact stability.

15

2. To manufacture a hybrid microcircuit active devices such as transistors and diods are mounted and bonded to substrate.

2. To be more economically competitive, more and more systems will incorporate micros.

2. Loaf semiconductor devices are known to be made by introducing controlled numbers of impurity atoms into a crystal.

3. Before discussing the patterns themselves it is necessary to exmine factors which are likely to intefere with the results.

2. The basic demand appears to be conductivity because it can substantially improve the resistance.

3. To form a film passive circuitry stripes of silver, aluminum or gold are grown by evaporation.

2. The structure of an integrated circuit is sure to be complex both in the topology of its surface and in its _я internal composition.

2. A thin film happens even to be employed to select the areas on a wafer that are to be oxidized. -

V. Ответьте на следующие вопросы:

1. What operations should be done before assembling?

2. What packages are used for intergrated circuits? 5. What are the types of packages?

4. What packages are designed to operate in adverse mechanical and environmental conditions?

4. What modifications does the second type have? 6. Describe the third type and its disadvantages. 7. Can the cane mounted on ceramic heads be only ceramic? 8. What are the advantages of flat packs?

VI. Переведите микротекст.

В зависимости от конструкции плоских корпусов при сборке могут применяться сварка, высокотемпературная пайка твердым припоем и пайка припойным стеклом. Основными достоинствами планарных корпусов являются малые размеры и масса, а также сравнительно высокое отношение площади кристалла к размерам корпуса.

VII. Составьте план текста на английском языке.

Кратко изложите в соответствии с планом содержание текста.

Используйте следующие выражения.

This text is about.... It introduces.... It advances the idea of... In conclusion... is given

VIII. Прочитайте текст со словарем, озаглавьте его и задайте 10 вопросов по содержанию текста.

In mounting a chip on the header, the chip is held with its gold-plated face down and then pressed onto the gold-plated header mounted on a header anvil, A eutectic such as a gold-silicon or gold-germanium alloy that forms under heat provides a good bond on cooling. All electrical connections are then made between the contact pads on the chip and lead-out pins of the header using thin gold wire attached by thermocompression bonding. This done, a gold-plated cover can is mounted on the header and hot-welded to form a sealed envelope.

There are other methods of bonding the chip to a header. In wide use is the flip chip method for attachment of active elements provided with ball leads, solder bumps, and beam leads. The method combines the operations of mechanical bonding and electrical connection of the chip to the header. This is essentially a thermocompression bonding method by which the chip is mounted, face down, onto the heated header and then pressed against it, so that the spider bumps (preliminarily built up on the chip) make contact with the conductor pattern and form soldered joints. Another method of bounding uses a lead frame to attact the chip to its spiderlike lead pattern. The method is rather simple end inexpensive.

High-power ICs require massive headers with external or built-in heat sinks to remove excess heat. The plastic package with a T-shaped heat sink allows the power dissipation of an 1C amplifier to be brought up to 6 W without overheating (for a common package, it reacts 1 W).

Each package bears on its surface, the designation of the 1C the date of manufacture, and the manufacturer's trade mark. To determine the lead number on the envelope the first lead is made to differ in shape from the others.