Economical assembly of small SMT batch sizes

For SMD prototyping or the production of small batches, the requirements for production equipment are different compared to that for mass production. The solutions used are mostly manual, semiautomatic or fully automatic equipment with high flexibility. A short changeover and set-up time is more important than speed during production.

Requirements for a high mix/low volume production
In the market segment of prototyping and the production of small batch size, high speed is not the highest priority. The production machines of interest must first of all be flexible to allow fast set-up and changeover from one product to another. The feeder capacity must be large so as to minimize the number of changeovers and it must be able to fulfill the requirements regarding application range and quality. For prototyping, the machinery must be easy to operate and set up, and must offer possibilities to produce a series of assemblies with acceptable quality.

In a production line for SMT assemblies, the technical requirements placed on the equipment depend on the application range. The high quality assembly of BGA or fine pitch components requires, of course, more advanced optical tools than the placement of standard SMD components. Today’s state-of-the-art production equipment can fulfill all requirements on a modular base. Especially for small- to mid-size companies, it is important to invest in a system which offers the required precision and quality, and the possibility to upgrade the equipmentwhen the demands grow.

Manual prototyping
Most small companies start their SMD assembly experience with a manual production line. While it is easy to understand that a manual pick and place and a small oven are indispensable for such a production process, the decision between dispensing or printing of solder paste may be harder to make.

Dispensing is very flexible and therefore the preferred solution for prototyping, but the technical limitation of a manual time-pressure dispenser is reached at a dot size of about 0.8mm (0603 chip components). While more advanced dispensing valves such as the Piezo-Flow Valve from Essemtec can reach much smaller dots, however, fine pitch dispensing can never reach the speed and reliabilityof stencil printing. Customers faced with the dilemma of very small batch sizes and fine pitch QFP usually draw acomplete line of solder paste over all the pads. This process,however, will require rework and cannot provide the samequality as printing.

The printing process becomes more economical above a certain batch size. To decide which technology should be used for a planned production, the manufacturing costs can be estimated using formula 1 and 2.

The result of the two calculations can best be explained graphically (figure 1). The break-even-point is the number of prints of one type where the costs of both production processes are equal. When the total number is bigger, then the printing process is more economical and a stencil should be made. The dispensing process should be used when the series size is smaller than break-even.

A complete modular manual production package consist of a screen/stencil printer, a manual pick and place system (preferably with dispenser option) and a batch reflow oven (figure 2) which offers all necessary features for the complete production of SMD boards. In this package, the high precision manual printer can be equipped with a guided double squeegee for fine-pitch printing, while the pick and place system offers the capability to place finepitch components and BGA. For prototyping, the placement head should have the capability of being equipped with a microprocessor-controlled time-pressure dispenser. The batch oven can offer preset profiles for a fast process setup and a high quality soldering process similar to large ovens.

Semi-automatic production
If more than just some prototypes must be produced or if the board is of high complexity then a semi-automatic production system will be the chosen solution. In such a system, some process steps, like the speed of the squeegee on a printer or the pickup and placement position on the assembly machine, can easily be controlled by a motor or a microprocessor.

A semi-automatic production package (figure 3) consists of a screen and stencil printer with motorized squeegee, a pick and place system with computer control and a conveyor or batch reflow oven. The aim is to increase production speed and also stability of product quality. To avoid huge rework costs and produce high quality continuously on the printing process, operator influence and control over all process parameters, such as squeegee pressure, angle and speed, must be reduced. The operator only places the board at the correct position, and the motorized squeegee will then deliver a process which is repeatable and therefore under control.

When assembling manually, missing components, misplacements and wrong component orientations can occur. These are errors which can be eliminated with a semiautomatic system such as the EXPERT-SA from Essemtec. Linear measurement systems in both axes control the position of the placement head accurately while the placement plan is stored in the connected computer, which guides the operator to the pick and placement position.

This guidance allows for speed and accuracy because no search time is needed as the orientation of the component is clearly indicated to ensure correct placement. Placement data may be imported directly from the CAD system, enabling fast programming and avoiding errors. This solution can also show its benefits when a single prototype of high complexity must be produced.

A semi-automatic production package can allow up to twice the production speed of a manual system and can also avoid a lot of repair and rework costs by eliminating assembly errors. It is usually chosen for the production of small series batches and SMD boards with a lot of components.

Automatic prototyping and high mix production
Production speed increases experienced using an automatic production line compared to manual production are significant. Placement rate and reliability may also increase, and cost and rework time can be saved.

Important requirements placed in automatic production equipment for high mix production include high flexibility, excellent quality, fast programming, quick set-up and changeover and the ability to place all kind of components. For small companies, additional factors of limited floor space and having the modularity to upgrade the machine with growing demands should be considered.

A possible solution is an automatic, standalone production package (figure 4) that includes a programmable automatic printer, a fully automatic pick and place system (with universal laser-centering and vision for BGA and QFP), an automatic dispensing system for glue or solder paste dispensing or encapsulation, and a conveyor reflow ovenwith preset reflow and curing program recommendations.

This automatic solution is economical even at relatively low production quantities. The saved operator costs, increased placement speed and quality are strong advantages compared to manual production. Together with the lower scrap and rework costs, it leads to much lower variable manufacturing costs.

Deciding factors
The larger the batch series and the more important the process control and stability, the higher will be the need for automation. It may also be a company’s strategy to invest in automatic systems, for example, to set up a CIM (computer integrated manufacturing) process or to install the required production capacity for future growth. Regardless of the reasons, no decision should be taken without first having economical proof. As production equipment is a key success factor, too small a capacity or too big an investment may have drastic consequences.

Comparison of production costs with different solutions shows whether a manual, a semi-automatic or an automatic solution is ideal for a planned production. The common procedure is to make a list of all possible costs like floor space, operator costs, electrical supply, air etc. Unfortunately, this generally does not work because either some costs cannot be separated correctly, they are not known or nobody has time to list them all. Additionally, the future is uncertain in detail. A more general calculation model with only the most important cost factors is the better approach, taking into account depreciation, personal cost, throughput, rework and expected volume. This analysis will in most cases clarify whether a manual, semiautomatic or an automatictool is the most economical solution (figure 5).

The production of SMD prototypes or small- to mid-size batch series requires above all flexible equipment. While solutions are available for manual, semiautomatic or fully automatic operation, in order to fulfill growing technical requirements, the equipment should be both modular and upgradeable.

Pick And Place Defects

Component Movement - It occurs basically due to the less amount of the paste or glue available to hold the component or due to improper dispense design.

Component Cracking - It occurs basically due to exccess force applied during placement or due to improper setting for double sided board.

Incorrect Placement - it occurs due to improper programming of the machine.

Misplaced Component - If the degree of error is same in all the boards then the program needs to be rectified or if it is different in boards then we have to check the setting of the machine.

Misplaced Pins - It is mainly caused due to improper handling of the components specially components in waffle.

SMT Placement

Surface mount components are placed on a printed circuit board after deposition of adhesive or solder paste. Placement equipment is commonly referred to as Pick And Place Equipment. The components can be placed on the board by

1. Manual placement
2. Automatic placement

MANUAL PLACEMENT

Manual placement of surface mount components is not reliable and can be used only for prototyping applications. The following are some of the problems associated with manual placement of components.

1. Most passive components do not have any part markings, and therefore, the possibility of part mix-up is very high.
2. Placement of components in wrong orientations due to operator related errors
3. Placement accuracy will again depends on the operator and it is very difficult to obtain good placement accuracy with manual placement.

In component placement, there are two main functions, pickup and placement. In manual placement, the components parts are picked up either by tweezers or by a vacuum pipette. For passive components tweezers are adequate, but for multi-leaded active devices, a vacuum pipette is very helpful in dealing with component rotation and is recommended when working with manual placement of components.

The following are the benefits of using manual placement machines

1. Very low capital cost
2. Ideal for prototype development due to low turnaround time and low cost
3. For low volume production manual pick and place machines with vacuum pickup and placement are preferred.

AUTOMATIC PLACEMENT

Automatic placement machines are required for high volume production as the manual method turnsout to be very slow. It is also possible to achieve consistent quality levels with automatic placement equipment. Vision capability is required for placement of fine-pitch components and it may add to the overall cost of the equipment. The following are the important parameters while selecting an automatic placement machine.

1. Placement speed

2. Requirement of placement of fine pitch or very fine pitch components

3. The variety of components that the machine should handle

5. Other features like CAD data downloading for reduction in programming time

6. Types of Feeder that the machine should support

7. Ability to dispense adhesive

8. Need for component testing

The user has to choose the placement machine appropriately depending on the application on hand and the future needs.

Surface-mount components are placed along the front (and often back) faces of the machine for the Inline Machines and for the Offline Machines the components can be loaded on all the four sides depending on the requirement. Most components, large and small are supplied on paper or plastic tape, the tape reels are loaded onto 'feeders', mounted to the machine. Larger ICs are sometimes supplied arranged in trays, which are stacked in a compartment on the machine for this purpose.

Through the middle of the machine there is a conveyor belt, along which unpopulated PCBs travel, and a PCB clamp in the centre of the machine. The PCB is clamped, and the nozzles pick up individual components from the feeders/trays, rotate them to the correct orientation and then place them on the appropriate pads on the PCB with a great deal of precision. Most Placement machines now can optically inspect components on picking, to ensure that the correct component has been picked, that it has been picked successfully and that it is in the correct rotational orientation. The components may be temporarily adhered to the PCB using the wet solder paste itself, or by using small blobs of a separate adhesive, applied by a glue dispensing machine.

~Once ~

My heart no longer beats the same

My lonely lips still speak your name

Tears are running down my face

Where once a kiss had left it's trace

I can't lay my head upon your chest

And feel my neck and hair caressed

My hands are bare without yours to hold

Where once the warmth replaced the cold.

I close my eyes with thoughts of you

Wishing that our time weren't through

The stars seem dim, there's no moonbeams

Where once we danced in all my dreams

And now nothing is as it was before

I have lost my love forevermore.

My soul is filled with emptiness

Where once I knew true happiness

I Have a Dream speech by Martin Luther King

Five score years ago, a great American, in whose symbolic shadow we stand signed the Emancipation Proclamation. This momentous decree came as a great beacon light of hope to millions of Negro slaves who had been seared in the flames of withering injustice. It came as a joyous daybreak to end the long night of captivity.
But one hundred years later, we must face the tragic fact that the Negro is still not free. One hundred years later, the life of the Negro is still sadly crippled by the manacles of segregation and the chains of discrimination. One hundred years later, the Negro lives on a lonely island of poverty in the midst of a vast ocean of material prosperity.
One hundred years later, the Negro is still languishing in the corners of American society and finds himself an exile in his own land. So we have come here today to dramatize an appalling condition.
In a sense we have come to our nation's capital to cash a check. When the architects of our republic wrote the magnificent words of the Constitution and the declaration of Independence, they were signing a promissory note to which every American was to fall heir. This note was a promise that all men would be guaranteed the inalienable rights of life, liberty, and the pursuit of happiness.
It is obvious today that America has defaulted on this promissory note insofar as her citizens of colour are concerned. Instead of honouring this sacred obligation, America has given the Negro people a bad check which has come back marked "insufficient funds." But we refuse to believe that the bank of justice is bankrupt. We refuse to believe that there are insufficient funds in the great vaults of opportunity of this nation. So we have come to cash this check -- a check that will give us upon demand the riches of freedom and the security of justice. We have also come to this hallowed spot to remind America of the fierce urgency of now. This is no time to engage in the luxury of cooling off or to take the tranquillising drug of gradualism. Now is the time to rise from the dark and desolate valley of segregation to the sunlit path of racial justice. Now is the time to open the doors of opportunity to all of God's children. Now is the time to lift our nation from the quick-sands of racial injustice to the solid rock of brotherhood.
It would be fatal for the nation to overlook the urgency of the moment and to underestimate the determination of the Negro. This sweltering summer of the Negro's legitimate discontent will not pass until there is an invigorating autumn of freedom and equality. Nineteen sixty-three is not an end, but a beginning. Those who hope that the Negro needed to blow off steam and will now be content will have a rude awakening if the nation returns to business as usual. There will be neither rest nor tranquillity in America until the Negro is granted his citizenship rights. The whirlwinds of revolt will continue to shake the foundations of our nation until the bright day of justice emerges.
But there is something that I must say to my people who stand on the warm threshold which leads into the palace of justice. In the process of gaining our rightful place we must not be guilty of wrongful deeds. Let us not seek to satisfy our thirst for freedom by drinking from the cup of bitterness and hatred.
We must forever conduct our struggle on the high plane of dignity and discipline. We must not allow our creative protest to degenerate into physical violence. Again and again we must rise to the majestic heights of meeting physical force with soul force. The marvellous new militancy which has engulfed the Negro community must not lead us to distrust of all white people, for many of our white brothers, as evidenced by their presence here today, have come to realize that their destiny is tied up with our destiny and their freedom is inextricably bound to our freedom. We cannot walk alone.
And as we walk, we must make the pledge that we shall march ahead. We cannot turn back. There are those who are asking the devotees of civil rights, "When will you be satisfied?" We can never be satisfied as long as our bodies, heavy with the fatigue of travel, cannot gain lodging in the motels of the highways and the hotels of the cities. We cannot be satisfied as long as the Negro's basic mobility is from a smaller ghetto to a larger one. We can never be satisfied as long as a Negro in Mississippi cannot vote and a Negro in New York believes he has nothing for which to vote. No, no, we are not satisfied, and we will not be satisfied until justice rolls down like waters and righteousness like a mighty stream.
I am not unmindful that some of you have come here out of great trials and tribulations. Some of you have come fresh from narrow cells. Some of you have come from areas where your quest for freedom left you battered by the storms of persecution and staggered by the winds of police brutality. You have been the veterans of creative suffering. Continue to work with the faith that unearned suffering is redemptive.
Go back to Mississippi, go back to Alabama, go back to Georgia, go back to Louisiana, go back to the slums and ghettos of our northern cities, knowing that somehow this situation can and will be changed. Let us not wallow in the valley of despair.
I say to you today, my friends, that in spite of the difficulties and frustrations of the moment, I still have a dream. It is a dream deeply rooted in the American dream.
I have a dream that one day this nation will rise up and live out the true meaning of its creed: "We hold these truths to be self-evident: that all men are created equal."
I have a dream that one day on the red hills of Georgia the sons of former slaves and the sons of former slave-owners will be able to sit down together at a table of brotherhood.
I have a dream that one day even the state of Mississippi, a desert state, sweltering with the heat of injustice and oppression, will be transformed into an oasis of freedom and justice.
I have a dream that my four children will one day live in a nation where they will not be judged by the colour of their skin but by the content of their character.
I have a dream today.
I have a dream that one day the state of Alabama, whose governor's lips are presently dripping with the words of interposition and nullification, will be transformed into a situation where little black boys and black girls will be able to join hands with little white boys and white girls and walk together as sisters and brothers.
I have a dream today.
I have a dream that one day every valley shall be exalted, every hill and mountain shall be made low, the rough places will be made plain, and the crooked places will be made straight, and the glory of the Lord shall be revealed, and all flesh shall see it together.
This is our hope. This is the faith with which I return to the South. With this faith we will be able to hew out of the mountain of despair a stone of hope. With this faith we will be able to transform the jangling discords of our nation into a beautiful symphony of brotherhood. With this faith we will be able to work together, to pray together, to struggle together, to go to jail together, to stand up for freedom together, knowing that we will be free one day.
This will be the day when all of God's children will be able to sing with a new meaning, "My country, 'tis of thee, sweet land of liberty, of thee I sing. Land where my fathers died, land of the pilgrim's pride, from every mountainside, let freedom ring."
And if America is to be a great nation this must become true. So let freedom ring from the prodigious hilltops of New Hampshire. Let freedom ring from the mighty mountains of New York. Let freedom ring from the heightening Alleghenies of Pennsylvania!
Let freedom ring from the snow-capped Rockies of Colorado!
Let freedom ring from the curvaceous peaks of California!
But not only that; let freedom ring from Stone Mountain of Georgia!
Let freedom ring from Lookout Mountain of Tennessee!
Let freedom ring from every hill and every molehill of Mississippi. From every mountainside, let freedom ring.
When we let freedom ring, when we let it ring from every village and every hamlet, from every state and every city, we will be able to speed up that day when all of God's children, black men and white men, Jews and Gentiles, Protestants and Catholics, will be able to join hands and sing in the words of the old Negro spiritual, "Free at last! free at last! thank God Almighty, we are free at last!"

The Quit India Speech By Mahatma Gandhi

The Quit India speech by Mahatma Gandhi

Before you discuss the resolution, let me place before you one or two things, I want you to understand two things very clearly and to consider them from the same point of view from which I am placing them before you. I ask you to consider it from my point of view, because if you approve of it, you will be enjoined to carry out all I say. It will be a great responsibility. There are people who ask me whether I am the same man that I was in 1920, or whether there has been any change in me. You are right in asking that question.
Let me, however, hasten to assure that I am the same Gandhi as I was in 1920. I have not changed in any fundamental respect. I attach the same importance to non-violence that I did then. If at all, my emphasis on it has grown stronger. There is no real contradiction between the present resolution and my previous writings and utterances.
Occasions like the present do not occur in everybody’s and but rarely in anybody’s life. I want you to know and feel that there is nothing but purest Ahimsa1 in all that I am saying and doing today. The draft resolution of the Working Committee is based on Ahimsa, the contemplated struggle similarly has its roots in Ahimsa. If, therefore, there is any among you who has lost faith in Ahimsa or is wearied of it, let him not vote for this resolution.
Let me explain my position clearly. God has vouchsafed to me a priceless gift in the weapon of Ahimsa. I and my Ahimsa are on our trail today. If in the present crisis, when the earth is being scorched by the flames of Himsa2 and crying for deliverance, I failed to make use of the God given talent, God will not forgive me and I shall be judged un-wrongly of the great gift. I must act now. I may not hesitate and merely look on, when Russia and China are threatened.
Ours is not a drive for power, but purely a non-violent fight for India’s independence. In a violent struggle, a successful general has been often known to effect a military coup and to set up a dictatorship. But under the Congress scheme of things, essentially non-violent as it is, there can be no room for dictatorship. A non-violent soldier of freedom will covet nothing for himself, he fights only for the freedom of his country. The Congress is unconcerned as to who will rule, when freedom is attained. The power, when it comes, will belong to the people of India, and it will be for them to decide to whom it placed in the entrusted. May be that the reins will be placed in the hands of the Parsis, for instance-as I would love to see happen-or they may be handed to some others whose names are not heard in the Congress today. It will not be for you then to object saying, “This community is microscopic. That party did not play its due part in the freedom’s struggle; why should it have all the power?” Ever since its inception the Congress has kept itself meticulously free of the communal taint. It has thought always in terms of the whole nation and has acted accordingly. . .
I know how imperfect our Ahimsa is and how far away we are still from the ideal, but in Ahimsa there is no final failure or defeat. I have faith, therefore, that if, in spite of our shortcomings, the big thing does happen, it will be because God wanted to help us by crowning with success our silent, unremitting Sadhana1 for the last twenty-two years.
I believe that in the history of the world, there has not been a more genuinely democratic struggle for freedom than ours. I read Carlyle’s French Resolution while I was in prison, and Pandit Jawaharlal has told me something about the Russian revolution. But it is my conviction that inasmuch as these struggles were fought with the weapon of violence they failed to realize the democratic ideal. In the democracy which I have envisaged, a democracy established by non-violence, there will be equal freedom for all. Everybody will be his own master. It is to join a struggle for such democracy that I invite you today. Once you realize this you will forget the differences between the Hindus and Muslims, and think of yourselves as Indians only, engaged in the common struggle for independence.
Then, there is the question of your attitude towards the British. I have noticed that there is hatred towards the British among the people. The people say they are disgusted with their behaviour. The people make no distinction between British imperialism and the British people. To them, the two are one This hatred would even make them welcome the Japanese. It is most dangerous. It means that they will exchange one slavery for another. We must get rid of this feeling. Our quarrel is not with the British people, we fight their imperialism. The proposal for the withdrawal of British power did not come out of anger. It came to enable India to play its due part at the present critical juncture It is not a happy position for a big country like India to be merely helping with money and material obtained willy-nilly from her while the United Nations are conducting the war. We cannot evoke the true spirit of sacrifice and velour, so long as we are not free. I know the British Government will not be able to withhold freedom from us, when we have made enough self-sacrifice. We must, therefore, purge ourselves of hatred. Speaking for myself, I can say that I have never felt any hatred. As a matter of fact, I feel myself to be a greater friend of the British now than ever before. One reason is that they are today in distress. My very friendship, therefore, demands that I should try to save them from their mistakes. As I view the situation, they are on the brink of an abyss. It, therefore, becomes my duty to warn them of their danger even though it may, for the time being, anger them to the point of cutting off the friendly hand that is stretched out to help them. People may laugh, nevertheless that is my claim. At a time when I may have to launch the biggest struggle of my life, I may not harbour hatred against anybody.

Vedas And Upnishads

The oldest literature of Indian thought is the Veda, a collection of religious and philisophical poems and hymns composed over several generations beginning as early as 3000 BC. The Veda was composed in Sanskrit, the intellectual language of both ancient and classical Indian civilizations. Four collections were made, so it is said that there are four Vedas. The four as a group came to be viewed as sacred in Hinduism.

Some Vedic hymns and poems address philosophic themes, such as the henotheism that is key to much Hindu theology. Henotheism is the idea that one God takes many different forms, and that although individuals may worship several different gods and goddesses, they really revere but one Supreme Being.

There are four Vedas:

The Rig-Veda
Its traditional date goes back to 3000 BC, something which the German scholar Max Mueller accepted. As a body of writing, the Rig-Veda (the wisdom of verses) is nothing short of remarkable. It contains 1028 hymns (10,589 verses which are divided into ten mandalas or book-sections) dedicated to thirty-three different gods. The most often addressed gods were nature gods like Indra (rain god; king of heavens), Agni (fire god), Rudra (storm god; the 'howler'), Soma (the draught of immortality, an alcoholic brew).

The Sama-Veda
The Sama-Veda or the wisdom of chants is basically a collection of samans or chants, derived from the eighth and ninth books of the Rig-Veda. These were meant for the priests who officiated at the rituals of the soma ceremonies. There are painstaking instructions in Sama-Veda about how particular hymns must be sung; to put great emphasis upon sounds of the words of the mantras and the effect they could have on the environment and the person who pronounced them.

The Yajur-Veda
The Yajur-Veda or the wisdom of sacrifices lays down various sacred invocations (yajurs) which were chanted by a particular sect of priests called adhvaryu. They performed the sacrificial rites. The Veda also outlines various chants which should be sung to pray and pay respects to the various instruments which are involved in the sacrifice.

The Atharva-Veda
The Atharva-Veda (the wisdom of the Atharvans) is called so because the families of the atharvan sect of the Brahmins have traditionally been credited with the composition of the Vedas. It is a compilation of hymns but lacks the awesome grandeur which makes the Rig-Veda such a breathtaking spiritual experience.

Upanishads

The term Upanishad ('upa' near; 'ni' down; 'sad' to sit) means sitting down near; this implies the students sitting down near their Guru to learn the big secret. In the splendid isolation of their forest abodes, the philosophers who composed the Upanishads contemplated upon the various mysteries of life and its creation – whether common, or metaphysical. The answers were however not open to all, but only for select students. The reason for this was simple: not everyone can handle knowledge.

The composition of the Upanishads marks a significant and stride forward in the direction of knowing the mystery of earth's creation and one comes tantalizingly close to the answers. Through episodes, commentaries, stories, traditions and dialogue, the Upanishads unfold the fascinating tale of creation, life, the essence of life and of that beyond to the seeker of truth.

There is no exact date for the composition of the Upanishads. They continued to be composed over a long period, the core being over 7th -5th centuries BC. The Upanishads were originally called Vedanta, which literally means the conclusion to the Vedas.

In the Upanishads, views about Brahman (the Absolute, or God) and atman (one's true self) were proposed.

There are 18 principal Upanishads viz:

Brhad-aranyaka Upanishad
The Brhad-aranyaka Upanishad is widely accepted to be the most important of all Upanishads. It has three khandas or parts. The madhu khanda contemplates on the relationship between the individual and the Universal self. The muni khanda or yajnavalkya is a debate which goes on to give the philosophical backing to the earlier teaching. The khila khanda tackles various rituals of worship and meditation.

Chandogya Upanishad
This Upanishad is a part of the Sama-Veda (see The Vedas). The name comes from the singer of the songs (samans) who is called Chandoga. The initial chapters of the Upanishad, discuss the ritual of sacrifice. The others debate the origin and profundity of the concept of Om, among other things.

Aitareya Upanishad
This one forms part of the Rig-Veda. The purpose is to make the reader understand the deeper meaning of sacrifice and to take him away from the outer trappings of the actual act.

Taittriya Upanishad
A part of the Yajur-Veda, this Upanishad is divided into three sections or vallis. The siksa valli deals with the phonetics of the chants, while the others, brahmananda valli and bhrgu valli deal with self-realization.

Isa Upanishad
Also called the Isavasya Upanishad, this book deals with the union of God, the world, being and becoming. The stress is on the Absolute in relation with the world (paramesvara). The gist of the teachings is that a person's worldly and otherworldly goals need not necessarily be opposed to each other.

Kena Upanishad
The name of this Upanishad comes from the first word kena, or by whom. It has two sections of prose and two of poetry. The verses deal with the supreme spirit or the absolute principle (brahmaana) and the prose talks of ishvara (god). The moral of the story is that the knowledge of ishvara reveals the way to self-realization.

Katha Upanishad
Also called the Kathakopanishad, this Upanishad uses a story (katha) involving a young Brahmin boy called Nachiketa to reveal the truths of this world and the other beyond the veil.

Prashna Upanishad
Prashna literally means question, and this book is part of the Athrava-Veda. It addresses questions pertaining to the ultimate cause, the power of Om, relation of the supreme to the constituents of the world.

Mundaka Upanishad
This book also belongs to the Atharva-Veda. The name is derived from 'mund' or to shave, meaning that anyone who understands the Upanishads is s(h)aved from ignorance. This book inscribes the importance of knowing the supreme brahmaana, only by which knowledge can one attain self-realization.

Mandukya Upanishad
The Mandukya is an exquisite treatise which expounds on the principle of Om and its metaphysical significance in various states of being, waking, dream and the dreamless sleep. The subtlest and most profound of the Upanishads, it is said that this alone will lead one to the path of enlightenment.

Svetasvatara Upanishad
The name of this Upanishad is after its teacher. It comments on the unity of the souls and the world in one all-encompassing reality. The concept of there being one god is also talked about here. It is dedicated to Rudra, the storm god.

Kausitaki Brahmana Upanishad
The Upanishad has come down to us in bits here and pieces there. The core of the text is dedicated to illustrating the fact that the path to release is through knowledge.

Maitri Upanishad
This is a comparatively later Upanishad as it has references to the Trinity of Hindu Gods (Shiva, Vishnu and Brahma) which is a later development, and plus references to the world being illusory in character reflects Buddhist influence.

Subala Upanishad
Belonging to the Yajur-Veda, this Upanishad puts down a dialogue between the sage Subala and Brahma the creator of the Hindu Trinity of Gods. It discusses the universe and the absolute.

Jabala Upanishad
Belonging to the Athrava-Veda this Upanishad addresses some questions pertaining to renunciation.

Paingala Upanishad
The Paingala is again a dialog, this between Yajnavalkya, the sage mentioned the Brhad-aranyaka's muni khanda and Paingala, a student of his. It discusses meditation and its effects.

Kaivalya Upanishad
This Upanishad delves into the state of kaivalya or being alone.

Vajrasucika Upanishad
Belonging to the Sama-Veda the Vajrasucika reflects on the nature of the supreme being.

The core of the teachings of the Upanishads is summed up in three words: tat tvam as… you are that.