Printed Circuit Board Manufacturing

Printed circuit boards are electronic circuits created by mounting electronic components on a nonconductive board, and creating conductive connections between them. The creation of circuit patterns is accomplished using both additive and subtractive methods. The conductive circuit is generally copper, although aluminum, nickel, chrome, and other metals are sometimes used. There are three basic varieties of printed circuit boards: single-sided, double-sided, and multi-layered. The spatial and density requirement and the circuitry complexity determine the type of board produced. Printed circuit boards are employed in the manufacturing of business machines and computers, as well as communication, control, and home entertainment equipment.

Production of printed circuit boards involves the plating and selective etching of flat circuits of copper supported on a nonconductive sheet of plastic. Production begins with a sheet of plastic laminated with a thin layer of copper foil. Holes are drilled through the board using an automated drilling machine. The holes are used to mount electronic components on the board and to provide a conductive circuit from one layer of the board to another.

Following drilling, the board is scrubbed to remove fine copper particles left by the drill. The rinse water from a scrubber unit can be a significant source of copper waste. In the scrubber, the copper is in a particulate form and can be removed by filtration or centrifuge. Equipment is available to remove this copper particulate, allowing recycle of the rinse water to the scrubber. However, once mixed with other waste streams, the copper can dissolve and contribute to the dissolved copper load on the treatment plant.

After being scrubbed, the board is cleaned and etched to promote good adhesion and then is plated with an additional layer of copper. Since the holes are not conductive,
electroless copper plating is employed to provide a thin continuous conductive layer over the surface of the board and through the holes. Electroless copper plating involves using chelating agents to keep the copper in solution at an alkaline pH. Plating depletes the metal and alkalinity of the electroless bath. Copper sulfate and caustic are added (usually automatically) as solutions, resulting in a .growth. in volume of the plating solution. This growth is a significant source of copper-bearing wastewater in the circuit board industry.

Treatment of this stream (and the rinse water from electroless plating) is complicated by the presence of chelating agents, making simple hydroxide precipitation ineffective. Iron salts can be added to break the chelate, but only at the cost of producing a significant volume of sludge.
Ion exchange is used to strip the copper from the chelating agent, typically by using a chelating ion exchange resin. Regeneration of the ion exchange resin with sulfuric acid produces a concentrated copper sulfate solution without the chelate. This regenerant can then be either treated by hydroxide precipitation, producing a hazardous waste sludge, or else concentrated to produce a useful product.

Growth from electroless copper plating is typically too concentrated in copper to treat directly by ion exchange. Different methods have been employed to reduce the concentration of copper sufficiently either to discharge the effluent directly to the sewer or to treat it with ion exchange. One method, reported by Hewlett-Packard, replenishes growth with formaldehyde and caustic soda to enhance its autocatalytic plating tendency, and then mixes it with carbon granules on which the copper plates out in a form suitable for reclaiming.

Following electroless plating a plating resist is applied to the panel and photo-imaged to create the circuit design. Copper is then electroplated on the board to its final thickness. A thin layer of tin lead solder or pure tin is plated over the copper as an etch resist. The plating resist is then removed to expose the copper not part of the final circuit pattern.

The exposed copper is then removed by etching to reveal the circuit pattern. Ammonia-based etching solutions are most widely used. Use of ammonia complicates waste treatment and makes recovery of copper difficult. An alternative to ammonia etching is sulfuric acid/hydrogen peroxide etching solutions. This latter etchant is continuously replenished by adding concentrated peroxide and acid as the copper concentration increases to about 80 g/L. At this concentration, the solution is cooled to precipitate out copper sulfate. After replenishing with peroxide and acid, the etchant is reused. Disadvantages of the sulfuric acid-peroxide etching solution are that it is relatively slow when compared with ammonia, and controlling temperature can be difficult.

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Printed Circuit Board Layout

Printed circuit board (PCB) design effort keeps growing as additional constraints such as rising clock frequencies, reduced area, increasing number of layers, mixed signal devices, and the ever increase in component numbers and densities. All of these factors combined have led to a steady rate of increase in development costs for current systems. As we design ever larger, denser and more complex systems, it is becoming increasingly difficult to estimate how much time would be required to design and verify them. To compound this problem, PCB design effort estimation still does not have a quantitative approach. We present in this paper a first step toward creating a design effort metric that is highly correlated with design effort for PCB layout. We follow the same approach taken in [1] as the principles that are applicable to microprocessors are also applicable to PCBs. In this paper, design effort corresponds to the number of engineering-hours required for implementation (layout) of a PCB design.

This paper analyzes and proposes various statistics to estimate the layout effort required to develop PCBs. We investigate and quantify statistics such as area, component count, pin count and device types and sizes for many PCBs. We analyze several of these statistics, and propose a metric, obtained after applying non-linear regression over the different statistics, which we call μPCBComplexity. In addition, we provide insights on the correlation between several statistics and design effort for several known layout design times. Different designs have different constraints, leading to specific challenges; typical design constraints being area, frequency, and cost. For example, having area being a primary design constraint, may lead to a requirement for additional layers, more expensive package types, and more complex placement and routing. A design constrained by cost, on the other hand, may require a balance between number of layers, area, drill density, types of packages and possibly the number of different drill sizes. Having clear constraints is necessary in estimating layout effort as it can drastically affect complexity. We define design effort to be the layout time required by one engineer. Design effort is equivalent to layout time when the project has a single developer, which is frequent even for complex PCBs. Nevertheless, for a given effort requirement, it is possible to reduce the design time by increasing the number of workers. Nevertheless, increasing the number of workers decreases the productivity per worker. The relationship between these two elements has been widely studied in software metrics and business models. Since the conversion between design effort and design time can be approximated, the remainder of this paper focuses only on design effort. The rest of the paper is organized as follows. Section 2 covers other work in this area; Section 3 describes the statistical techniques that allow us to calibrate and evaluate the μPCBComplexity regression model; Section 4 describes the setup for our evaluation; Section 5 evaluates several statistics for the boards in our analysis; and Section 6 presents conclusions and future work.

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OVERVIEW OF PCB TYPES

A PCB consists of a nonconducting substrate (typically fiberglass with epoxy resin) upon which a conductive pattern or circuitry is formed. Copper is the most prevalent conductor, although nickel, silver, tin, tin-lead, and gold may also be used as etch-resists or top-level metal. There are three types of PCBs: single-sided, double-sided, and multilayer. Single-sided boards have a conductive pattern on one side only, double-sided boards have conductive patterns on both faces, and multilayer boards consist of alternating layers of conductor and insulating material bonded together. The conductive layers are connected by plated through-holes, which are also used to mount and electrically connect components. PCBs may also be either rigid, flexible, or a combination of the two (rigid-flex).

Three Types of PCBs

SINGLE-SIDED PCB

Several critical manufacturing steps are not included in the typical single-sided manufacturing sequence and no process is unique to single-sided production. Therefore, any manufacturer of double-sided or multilayer PCBs can produce single-sided ones as well. Few shops produce single-sided panels exclusively, but instead include single-sided panels as part of their overall product mix. The most common sequence of single-sided production is drill, print-and-etch, surface finish, and final fabrication (all of these production processes are explained in Section 203). No inner-layer processing is required, and desmear is also eliminated. Furthermore, only in rare cases are plated through-holes required; therefore, all of the processes required to make the holes conductive are not applicable to single-sided manufactures. The holes instead provide mechanical stability for through-hole panels. Drilling may be completely eliminated on single-sided PCBs if the components are all surface-mounted.

DOUBLE-SIDED PCB
Not unlike single-sided, double-sided PCB manufacturing is also a subset of the multilayer process. The inner layer image transfer, lamination, and hole cleaning process are not performed. Therefore, any multilayer manufacturer can easily produce double-sided panels. Double-sided PCBs require electroless copper or other methods of making holes conductive, since the top and bottom sides of the board require interconnection.


MULTILAYER PCB

Single- and double-sided manufacturing processes are
subsets of the multilayer process. Therefore the multilayer manufacturing process will be described in detail in Section 205. Multilayer boards represent two-thirds of the overall value of U.S. production dollars, even though they are produced in lower numbers
than single- or double-sided PCBs. The rigid multilayer process (rigid PCBs) represent about 95% of U.S. production.

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Printed Circuit Board Manufacturing Industry Profile

Manufacturers of printed circuit boards (PC boards) are included as part of the electronic component manufacturing industry. As of 1984, the printed circuit board manufacturing industry consisted of a total of 585 plants with an employment of 435,100 (NCO 1984). Industry personnel indicate that the actual number of plants may be closer to 1,000 (USEPA 1986). The industry consists of large facilities totally dedicated to printed circuit boards, large and small captive facilities, small job shops doing contract work, and specialty shops doing low-volume and high-volume precision work. Approximately half of the printed circuit boards produced are by independent producers, while the rest are by captive producers. Over 65 percent of all printed circuit board manufacturing sites are located in the northeastern states and in California (NCO 1984). The printed circuit board manufacturers visited as a part of this study are all considered small. Generally, these small companies can be characterized as those that produce up to 3,000 to 5,000 square feet of processed board each month and require approximately 8,000 to 10,000 square feet of building space. Large companies can be characterized as those that produce or 30,000 to 50,000 square feet per month.

Products and Their Use
Printed circuit boards can be classified into three basic types: single-sided, double-sided, and multi-layered. The total board production in 1983 was 14 million square meters (PEI 1983). Double-sided boards accounted for about 55 percent of the printed circuit boards produced, while multi-layer board production made up 26 percent (PEI 1983). The type of board produced depends on the spatial and density requirement, and on the complexity of the circuitry. Printed circuit boards are used mainly in the production of business machines, computers, communication equipment, control equipment and home entertainment equipment.
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PCB Testing – Prevention Is Always Better

PCB’s find their application in electronic appliances like DVD, Televisions, cell phones, computers, calculators, watches, but to name a few. These appliances would not function if the PCB is not functioning; hence it is very important to test the PCB’s to check their reliability and performance before they are applied in these multifarious industries.
The testing process includes the bare board tests in which the unpopulated circuit boards are required to undergo and every connection is checked on the finished circuit board as correct. In case of mass production of circuit boards , the testing is done using a bed of nails tests or fixture where they are connected with the copper holes or lands present on either one or both sides of the board, so that the testing process is managed easily. Then with the use of computer electric testing unit, current in a small quantity is send on the nail bed through every point of contact thus ensuring that current is detected on appropriate contact points.

Even after the board is populated it has to be tested by different methods that include manual inspection of the PCB, optical inspection, analog signature analysis, and power off testing which is done when the electric current is not passed. When the power is on, the tests that are carried out are the in-circuit test which is done to test the voltage and frequency & the functional test wherein the PCB is tested for functionality.

After the process of testing is complete, the PCB’s which fail to work are disordered by the technicians and the components of the PCB are replaced through a process known as rework.

The process of PCB testing is a very significant process and is always given equal amount of importance as the manufacturing process. Imagine a well known brand, a well established brand having problems with its electronic goods. The brands reputation would be put to risk; moreover the customer may also lodge a complaint through the consumer court which would hinder the brands reputation adversely.

PCB Testing is more like an investment wherein you are assured of quality at a little overhead. So, it is very important to manage the testing activity. If you are outsourcing this activity always ensure the credibility of the testing company through their past records. Always take care of the quality of PCB’s by avoiding companies that are inexpensive ones, consider the quality service.

Whether it is a PCB or some other product, testing is always a good policy.

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PCB Fabrication - Printed Circuit Board Fabrication Is Possible At Home Also

PCB fabrication for multiple layered printed circuit boards is managed with an objective of providing an extra degree of freedom when it comes to selecting complicated or noise sensitive electronic circuits. The process includes the stacking of circuits on one another to establish predetermined interconnection set amongst them, with the help of reliable and techniques used for the sole purpose.

It is even possible to manage PCB fabrication at home and the benefit of making one at home is solving problems related to complex circuits. The method of PCB fabrication at home is as follows:

In the first stage the magazine schematic is transferred to the layout programs schematic part. This is followed by utilizing the PCB layout program to place the parts on board as well as to manage the routing of computer traces. After completion of some parts, clearance of rat’s nets begins. After the layout is done, a laser printer manages the printing of the board layers on a special toner transfer paper. The process of transferring the board image on the bare copper board is done with the help of a laminating machine or an iron that is used for hot cloth ironing.

Then the board is kept under water so that the paper that has stuck to can be removed and the toner remains behind. For the etching activity, an aquarium is used. Two aquarium pumps move over the copper boards while the job of the two aquarium heaters is to maintain the temperatures at 110 F. Depending upon the copper thickness as well as the quality of the solution, this activity can be managed in around 30 minutes on a higher end.

Once the etching work is completed, a solvent is utilized for removing the toner and the tinning process is managed using a soldering iron as well as a small tinned solder wick piece. Though, tinning is not mandatory, even though, it is advisable because it enhances the appearance of the board as well as prevents the oxidation process of copper until the process of soldering parts of board is done.
Then, the drilling of holes for leaded components and mounting holes is managed. Finally, the board is completely read to be populated.

The PCB fabrication process can be successfully managed if each and every step is carefully executed as well as the quality of the material used in the fabrication also plays an important role. So, if you are planning to create a durable PCB then it is important to keep the quality aspect in mind always.

Some of the points to be kept in mind while choosing a quality and etchant system, a good etchant system will result in a good quality fabrication. Etchants like FeCI3, Chromic acid, cupric chloride etc are some of the popularly used ones.

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PCB Design Software – The Easy Way Out

When searching for a high end PCB designs software, there are various aspects to be kept in mind so that the product you get is loaded with the required facilities at a reasonable price. Though if the product is good there is no harm in paying a bit more bucks.

Before buying a PCB design software it’s necessary to review your requisites. The software should provide facilities like easy to use interface, manual routing or auto rooting tools and automatic placers. The software should have the facility of creating new parts and footprints, a standard library wherein you can share designs, multi-level hierarchy with schematic capture as well as export the Spice, Net list or PCB layout. The most important of all is an easy to grasp tutorial which will simplify your PCB manufacturing activity.

There are a variety of software’s available in the market that provides most of the above mentioned facilities and features like

User Friendly Interface - This feature supports multispeed and schematic software’s and makes schematic design in a very simple and speedy process which can be managed simply by selecting and placing components on your documents and interconnecting them with the help of wire and bus tools. There is a tutorial which takes you through each and every step of PCB designing.

Automatic Routing Facility – This feature allows the routing of complicated layouts SMD components and single layer boards too. There are software’s that have two different routers, shape based router and grid based router which can be used for making single layer boards with jumper wires. These software’s support curved tracing and editing the traces to any degree.

Advance Testing Facility – This feature allows the testing of the schematic and PCB modules thus controlling the quality of the project at each and every phase. Functions like DRC and ERC provide a check on the inter-clearance of design objects as well as checks for errors in schematic pin connections. The facility includes the presentation of these errors in a graphical format so that the fixation of the errors can also be carried out flawlessly at every step. Features like net connective test the PCB’s or electrical connectivity.

Sharing Facility – With the help of this feature it is possible to exchange layouts, schematics and the libraries with other EDA and CAD packages

Many other features like spice support, support for manufacture of output formats etc have to be present with the design software you are purchasing. If the PCB design software is good the product would be of best quality so always compare the features of the shortlisted companies from where you are willing to buy the software and then purchase it.

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