Circuit board

- Nov 09, 2019-

Circuit board

Printed circuit boards, also known as printed circuit boards, printed circuit boards, often use the English abbreviation PCB (Printed circuit board), is an important electronic component, is the support of electronic components, is the provider of electronic components line connection. Because it is made using electronic printing technology, it is called a "printing" circuit board.


Prior to the advent of printed circuit boards, the interconnection between electronic components relied on wires to form a complete line. Today, circuit breadboards exist only as an effective experimental tool, and printed circuit boards have become the dominant position in the electronics industry. At the beginning of the 20th century, in order to simplify the production of electronic devices, reduce the wiring between electronic components, and reduce the manufacturing cost, the method of replacing wiring by printing was started. For thirty years, engineers have been proposing to wire metal conductors on insulated substrates. The most successful is that in 1925, the United States Charles Ducas printed a circuit pattern on an insulated substrate, and then successfully established a conductor for wiring by electroplating. [1]

Until 1936, the Austrian Paul Eisler published foil technology in the UK [1], he used a printed circuit board in a radio device; in Japan, Miyamoto Hiroyuki sprayed wiring The law "small method of blowing the wiring method (license 119384)" successfully applied for a patent. [2] In the two, Paul Eisler's method is most similar to today's printed circuit boards. This type of practice is called subtraction, which removes unwanted metals. Charles Ducas and Miyamoto's approach is only added. The wiring required is called the additive method. Even so, because the electronic components at that time generated a large amount of heat, the substrates of the two were difficult to use [1], so that there was no formal use, but the printed circuit technology was further improved.

History of development

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In 1941, the United States painted copper paste on talc for wiring to make a proximity tube.

In 1943, Americans used the technology extensively in military radios.

In 1947, epoxy resins began to be used as substrates for fabrication. At the same time, NBS began to study the manufacturing technology of coils, capacitors, resistors, etc. by printed circuit technology.

In 1948, the United States officially recognized the invention for commercial use.

Since the 1950s, transistors with lower heat generation have largely replaced the status of vacuum tubes, and printed circuit board technology has only begun to be widely adopted. At that time, the etched foil technology was the mainstream [1].

In 1950, in Japan, silver lacquer was used as a wiring on a glass substrate, and copper foil was used as a wiring on a paper phenolic substrate (CCL) made of a phenol resin. [1]

In 1951, the appearance of polyimide made the heat resistance of the resin further, and a polyimide substrate was also produced. [1]

In 1953, Motorola developed a double panel with a plated through hole method. This method is also applied to later multilayer boards. [1]

Printed circuit boards were widely used 10 years later in the 1960s, and their technology is becoming more mature. Since the introduction of Motorola's dual-panel, multi-layer printed circuit boards have begun to appear, increasing the ratio of wiring to substrate area.

In 1960, V. Dahlgreen applied a circuit-coated metal foil film to a thermoplastic plastic to create a flexible printed circuit board. [1]

In 1961, Hazeltine Corporation of the United States made a multi-layer board by referring to the plated through-hole method. [1]

In 1967, "Plated-up technology", one of the method of layering, was published. [1][3]

In 1969, FD-R made flexible printed circuit boards from polyimide. [1]

In 1979, Pactel published the "Pactel Method", one of the methods of layering. [1]

In 1984, NTT developed the "Copper Polyimide Method" for thin film circuits. [1]

In 1988, Siemens developed the multilayer printed circuit board of Microwiring Substrate. [1]

In 1990, IBM developed a layered printed circuit board for the Surface Laminar Circuit (SLC). [1]

In 1995, Matsushita Electric developed a layered printed circuit board for ALIVH. [1]

In 1996, Toshiba developed a B2it build-up printed circuit board. [1]

Practical

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In the late 1990s, when a number of build-up printed circuit board solutions were proposed, the build-up printed circuit boards were officially and largely put into practical use until now. It is important to develop a robust test strategy for large, high-density printed circuit board assemblies (PCBA) to ensure compliance and functionality. In addition to the establishment and testing of these complex assemblies, the amount of money invested in electronic components can be very high - up to $25,000 when a unit is tested. Because of this high cost, the problem of finding and repairing assemblies is now even more important than in the past. Today's more complex assembly is approximately 18 square inches, 18 layers; there are more than 2,900 components on the top and bottom; 6,000 circuit nodes; more than 20,000 solder joints to be tested.

range

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Manufactured and tested state-of-the-art PCBA and complete conveyor systems at Lucent's accelerated manufacturing facility (N. Andover, MA). Assembly with more than 5000 nodes is a concern for us because they are close to the resource limits of our existing ICT (in circuit test) devices (Figure 1). We now manufacture about 800 different PCBAs or "nodes". Of the 800 nodes, about 20 are in the range of 5000 to 6000 nodes. However, this number has grown rapidly.

new project

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New development projects require more complex, larger PCBAs and tighter packaging. These requirements challenge our ability to build and test these units. Furthermore, larger boards with smaller components and higher node counts will likely continue. For example, one design that is currently drawing a board diagram has approximately 116,000 nodes, more than 5100 components, and more than 37,800 solder joints that require testing or validation. This unit also has a BGA on the top and bottom, and the BGA is followed. One method of ICT is not possible using a conventional needle bed to test this size and complexity of the board.

Increasing PCBA complexity and density is not a new issue in manufacturing processes, especially in testing. Realizing that increasing the number of test pins in the ICT test fixture is not the direction to go, we began to observe alternative circuit confirmation methods. Seeing the number of contacts per million probes, we found that at 5000 nodes, many of the errors found (less than 31) may be due to probe contact problems rather than actual manufacturing defects (Table 1). Therefore, we set out to reduce the number of test pins instead of rising. Despite this, the quality of our manufacturing process is still assessed throughout the PCBA. We decided to use a combination of traditional ICT and X-ray stratification as a viable solution.

Substrate

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The substrate is generally classified by the insulating portion of the substrate. Common raw materials are electric wood, fiberglass, and various plastic plates. Manufacturers of PCBs generally use an insulating part composed of glass fiber, non-woven material, and resin, and then press it into a "prepreg" with epoxy resin and copper foil.

The common substrates and main ingredients are:

FR-1 ─ phenolic cotton paper, this substrate is commonly known as bakelite (higher economy than FR-2)

FR-2 ─ phenolic cotton paper,

FR-3 ─ Cotton paper, epoxy resin

FR-4 ─ Woven glass, epoxy resin

FR-5 ─ glass cloth, epoxy resin

FR-6 ─ matte glass, polyester

G-10 ─ glass cloth, epoxy resin

CEM-1 ─ cotton paper, epoxy resin (flame retardant)

CEM-2 ─ cotton paper, epoxy resin (non-flame retardant)

CEM-3 ─ glass cloth, epoxy resin

CEM-4 ─ glass cloth, epoxy resin

CEM-5 ─ glass cloth, polyester

AIN - aluminum nitride

SIC - Silicon Carbide

Metal coating

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In addition to the wiring on the substrate, the metal coating is where the substrate wiring is soldered to the electronic components. In addition, different metals have different prices, and different ones will directly affect the cost of production; different metals also have different solderability, contact properties, and different resistance values, which will directly affect the performance of components.

Commonly used metal coatings are:

copper

tin

The thickness is usually 5 to 15 μm [4]

Lead-tin alloy (or tin-copper alloy)

That is, the solder is usually 5 to 25 μm thick and the tin content is about 63% [4]

gold

Generally only plated on the interface [4]

silver

Generally only plated at the interface, or alloyed with silver as a whole

Line design

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The design of the printed circuit board is based on the electronic circuit diagram, which realizes the functions required by the circuit user. Printed circuit board design mainly refers to the layout design, which requires internal electronic components, metal wiring, through-hole and external connection layout, electromagnetic protection, heat dissipation, crosstalk and other factors. Excellent circuit design can save production costs and achieve good circuit performance and heat dissipation. Simple layouts can be implemented manually, but complex circuit designs typically require computer-aided design (CAD), and well-known design software includes Protel, OrCAD, PowerPCB, and FreePCB.

Basic production

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Introduction

According to different technologies, it can be divided into two major categories of processes.

Subtraction method

Subtractive is the removal of unwanted areas on a blank circuit board (ie, a circuit board covered with a complete piece of metal foil) using chemicals or machinery. The remaining convenience is the required circuit.

Screen printing: The pre-designed circuit diagram is made into a mesh screen. The unnecessary circuit parts on the screen are covered with wax or impervious material. Then the screen mask is placed on the blank circuit board and then on the wire. The protective agent that will not be corroded on the oil on the net will put the circuit board into the corrosive liquid. The part not covered by the protective agent will be eroded away, and finally the protective agent will be cleaned.

Photosensitive plate: The pre-designed circuit diagram is made on a light-transmissive film mask (the simplest method is to use the printer to print the slide). Similarly, the required part should be printed as an opaque color, and then in the blank line. The board is coated with photographic pigment, and the prepared film mask is placed on the circuit board to illuminate the glare for a few minutes. After removing the mask, the pattern on the circuit board is displayed with the developer, and finally, as with the screen printing method. Corrode the circuit.

Marking: Use the milling machine or laser engraving machine to directly remove unwanted parts of the blank line.

Addition method

Additive, now commonly used on a substrate pre-plated with thin copper, covered with photoresist (D / F), exposed to ultraviolet light and then developed, exposed where needed, and then used to plate the circuit board On the official line, the copper thickness is thickened to the required specifications, and then an anti-etching resist-metal thin tin is applied, and finally the photoresist is removed (this process is called film removal), and then the copper foil under the photoresist is applied. The layer is etched away.

Laminated method

[1] The laminate method is one of the methods for making multilayer printed circuit boards. The outer layer is wrapped after the inner layer is made, and the outer layer is treated by subtraction or addition. By repeating the operation of the lamination method, it is possible to obtain a multilayer multilayer printed circuit board which is a sequential lamination method.

Inner layer production

Multi-layered (ie, the action of bonding different layers)

Finishing is completed (subtraction of the outer metal foil film; addition method)

drilling

Subtraction method

Panel plating

Full block PCB plating

Add a barrier layer to the surface where it is to be retained (resist)

Etching

Removal of barrier layer

Pattern plating

In the place where the surface is not to be retained, the barrier layer is added.

Electroplating required surface to a certain thickness

Removal of barrier layer

Etching to unwanted metal foil film disappears

Addition method

Roughening the surface

Full-additive

Add a barrier layer where there is no conductor

Making lines with electroless copper

Partial addition method (semi-additive)

Covering the entire PCB with electroless copper

Add a barrier layer where there is no conductor

Electrolytic copper plating

Removal of barrier layer

Etching until the original electroless copper disappears under the barrier layer

Layering method

The layering method is one of the methods for making a multilayer printed circuit board. As the name implies, the printed circuit board is layer by layer. Each layer is added to the desired shape.

ALIVH

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[1]

ALIVH (Any Layer Interstitial Via Hole, Any Layer IVA) is a layer-adding technology developed by Matsushita Electric Industrial Co., Ltd. This is based on the use of an aramid fiber cloth.

Immerse the fiber cloth in epoxy resin to become a "prepreg"

Laser drilling

Filling the hole with conductive paste

Adhesive copper foil on the outer layer

Circuit pattern is formed by etching on copper foil

Adhering the semi-finished product that completes the second step to the copper foil

Layered

Repeat steps 5 through 7 until you are finished

B2it

[1]

B2it (Buried Bump Interconnection Technology) is a layering technology developed by Toshiba.

Make a double or multi-layer board first

Printing cone silver paste on copper foil

Put the adhesive on the silver paste and let the silver paste penetrate the adhesive sheet

Stick the adhesive sheet from the previous step on the board of the first step

Etching the copper foil of the adhesive sheet into a circuit pattern

Repeat steps 2 through 4 until you are finished

ways to produce

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Introduction

Both SMT and DIP are ways to integrate parts on the PCB. The main difference is that SMT does not need to drill holes in the PCB. In DIP, the PIN pin of the part needs to be inserted into the hole that has been drilled.

SMT (Surface Mounted Technology)

Surface mount technology mainly uses the placement machine to mount some micro-miniature parts onto the PCB. The production process is: PCB board positioning, printing solder paste, placement machine placement, over-reflow oven and inspection. With the development of technology, SMT can also mount some large-sized parts, for example, some large-sized mechanical parts can be mounted on the motherboard.

SMT integration is sensitive to positioning and part size, and solder paste quality and print quality also play a key role.

DIP

DIP is the “plug-in”, which is to insert parts on the PCB version. Because the parts are large in size and not suitable for placement or the manufacturer's production process cannot use SMT technology, the parts are integrated in the form of plug-ins. At present, there are two implementations of manual plug-ins and robot plug-ins in the industry. The main production process is: adhesive backing (

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