Manufacture of printed circuit board

Substrates are generally classified by the insulating part of the substrate, and the common raw materials are bakelite, glass fiber board and various plastic boards. PCB manufacturers generally use insulating parts composed of glass fiber, non-woven fabric and resin, and then press them into "prepreg" with epoxy resin and copper foil.

The common substrates and main components of Xgs game machine circuit design are:

FR- 1 ── Phenolic cotton paper, commonly known as bakelite (more economical than FR-2).

FR-2 ── Phenolic cotton paper,

FR-3 ── Cotton Paper and Epoxy Resin

FR-4 ── Epoxy glass fiber fabric

FR-5 ── Glass Cloth and Epoxy Resin

FR-6 & Frosted Glass and Polyester

G- 10 ── epoxy glass cloth

CEM- 1 ── Cotton paper and epoxy resin (flame retardant)

CEM-2-Cotton Paper and Epoxy Resin (Non-Flame Retardant)

CEM-3 ── Glass cloth and epoxy resin

CEM-4 ── Glass cloth and epoxy resin

CEM-5 ── Glass cloth and polyester

aluminium nitride

SiC-SiC metal coating is not only the wiring on the substrate, but also the place where the circuit of the substrate is soldered with electronic components. In addition, the price of different metals is different, which directly affects the production cost. In addition, the solderability, contact and resistance of each metal are different, which will directly affect the performance of components.

Commonly used metal coatings are: copper, tin (usually with a thickness of 5 to 15μm), lead-tin alloy (or tin-copper alloy, namely solder, with a thickness of 5 to 25μm and a tin content of about 63%), gold (usually only plated on the interface) and silver (usually only plated on the interface, or an alloy containing silver as a whole). According to different technologies, it can be divided into two categories: elimination and addition.

subtraction

Subtraction method is to use chemicals or machinery to remove unnecessary parts from a blank circuit board (that is, a circuit board covered with a whole piece of metal foil), and the rest is the circuit that is convenient for need.

Screen printing: make the pre-designed circuit diagram into a screen mask, and the unnecessary circuit parts on the screen will be covered by wax or impermeable materials. Then, put the screen mask on a blank circuit board, coat the screen with a protective agent that will not corrode, put the circuit board into an corrosive solution, and the parts not covered by the protective agent will be corroded. Finally, clean the protective agent.

Photosensitive board: Make the pre-designed circuit diagram on a transparent film mask (the easiest way is to print the slides with a printer), then print the required parts into opaque colors, then apply photosensitive pigments on the blank circuit board, put the prepared film mask on the circuit board for a few minutes with strong light, remove the mask and display the pattern on the circuit board with developer, and finally corrode the circuit like screen printing.

Engraving: Use milling machine or laser engraving machine to directly remove the unnecessary parts on the blank circuit.

Addition process

In the addition process, it is common to cover a thin copper substrate with photoresist (D/F) in advance, expose it with ultraviolet light and develop it to expose the required places, then thicken the copper thickness of the formal circuit on the circuit board to the required specifications by electroplating, then coat it with a thin layer of metal tin, finally remove the photoresist (this process is called stripping), and then etch off the copper foil layer under the photoresist.

Lamination method

Lamination method is one of the methods to make multilayer printed circuit boards. After the inner layer is finished, the outer layer is wrapped, and then the outer layer is processed by subtraction or addition. When the sequential lamination method is used, the operation of the lamination method is repeated, and a multilayer printed circuit board can be obtained.

1. Inner layer manufacturing

2. Laminated knitting (i.e. the act of bonding different layers)

3. Lamination is completed (minus the outer layer of the metal foil film; Addition process)

drill

Panel method

1. whole plate electroplating

2. Add a resist where the surface is to be preserved (to prevent it from being etched).

etch

Step 4 remove the barrier layer

Pattern method

1. Add a barrier layer where the surface is not reserved.

2. Electroplate the required surface to a certain thickness.

Step 3 remove the barrier layer

4. Etching until the unnecessary metal foil film disappears.

Complete addition process

1. Add barrier layers where conductors are not needed.

2. The circuit consists of electroless copper plating.

Part of the addition process

1. Cover the whole PCB with electroless copper plating.

2. Add a barrier layer where the conductor is not needed.

3. Electroplating copper

Step 4 remove the barrier layer

5. Etching until no electrolytic copper disappears under the barrier layer.

ALIVH

Alivh (Intermittent Via with Arbitrary Layer, IVA with Arbitrary Layer) is a layer adding technology developed by Panasonic. This is based on aramid fiber cloth.

1. Soak fiber cloth in epoxy resin to become "prepreg".

2. Laser drilling

3. Fill the hole with conductive adhesive.

4. Stick copper foil on the outer layer

5. Making circuit patterns on copper foil by etching.

6. Stick the semi-finished product after the second step on the copper foil.

Step 7: Combination knitting

8. Repeat steps 5 to 7 until complete.

B2it

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

1. First, make a double panel or multilayer board.

2. Printing tapered silver paste on copper foil

3. Put the adhesive sheet on the silver paste so that the silver paste flows through the adhesive sheet.

4. Stick the adhesive sheet of the previous step on the board of the first step.

5. The copper foil of the adhesive sheet is made into a circuit pattern by etching.

6. Repeat steps 2-4 until denser PCB, higher bus speed and analog RF circuit all pose unprecedented challenges to the test. Functional testing in this environment requires careful design, thoughtful testing methods and appropriate tools to provide credible test results.

When dealing with fixture suppliers, we should keep these problems in mind and think about where the products will be made, which is something that many test engineers will ignore. For example, let's assume that the test engineer is in California, but the product is made in Thailand. Test engineers will think that products need expensive automatic fixtures, because factories in California are expensive, and the fewer testers are needed, the better. Using automatic fixtures can reduce the employment of high-tech and high-paying operators. But in Thailand, these two problems do not exist, so it is cheaper to solve these problems manually, because the labor cost here is very low and the land price is very cheap, and large factories are not a problem. So sometimes first-class equipment may not be popular in some countries.

Engineering level

In high-density UUT, if calibration or diagnosis is needed, manual exploration is likely to be needed. This is because the needle bed contact is limited and the test speed is faster (testing UUT with probe can collect data quickly instead of feeding information back to the edge connector), so operators need to explore the test points on UUT. No matter where you are, make sure that the test sites are clearly marked.

Probe types and ordinary operators should also pay attention to the following issues:

Is the probe larger than the test point? Is the probe in danger of short-circuiting several test points and damaging UUT? Is there any danger of electric shock to the operator?

Can each operator quickly find out the test points and check them? Is the test center big and easy to identify?

How long does it take the operator to press the probe on the test point to get an accurate reading? If the time is too long, there will be some troubles in the small test area, such as the operator's hand slipping because of the long test time. It is suggested to expand the test area to avoid this problem.

After considering the above problems, the test engineer should re-evaluate the types of test probes, modify the test documents to better determine the location of test points, and even change the requirements for operators.

automatic detection

In some cases, automatic detection will be needed, for example, when it is difficult to detect PCB manually, or when the test speed is greatly reduced due to the technical level of operators, the automatic method should be considered.

Automatic detection can eliminate human error, reduce the possibility of short circuit at several test points and speed up the test operation. However, we should be aware that automatic detection may have some limitations, which vary according to the design of the supplier, including:

Area of UUT

Number of synchronous detectors

How close are the two test sites?

Test the positioning accuracy of the probe

Can the system detect UUT on both sides?

How fast does the probe move to the next test point?

What is the actual spacing required by the probe system? Generally speaking, it is larger than the off-line functional test system.

Automatic inspection usually does not use the needle bed fixture to touch other test points, which is generally slower than the production line, so it may take two steps: if the detector is only used for diagnosis, the traditional function test system can be considered on the production line, and the detector can be placed next to the production line as a diagnosis system; If the purpose of the detector is UUT calibration, then the only real solution is to use multiple systems, which is much faster than manual operation.

How to integrate into the production line is also a key issue that must be studied. Is there room on the production line? Can the system be connected to the conveyor belt? Fortunately, many new detection systems are compatible with the SMEMA standard, so they can work in an online environment.

Boundary scanning

This technology should be discussed as early as the product design stage because it requires special components to perform this task. In UUT with digital circuit as the main body, devices supporting IEEE 1 194 (Boundary Scan) can be purchased, so that most diagnosis problems can be solved with little or no detection. Boundary scan will reduce the overall function of UUT, because it will increase the area of each compatible device (4 ~ 5 pins and some wires per chip), so the principle of choosing this technology is to improve the diagnosis result at cost. It should be remembered that boundary scan can be used to program flash memory and PLD devices on UUT, which further increases the reason for choosing this test method.

How to deal with a limited design?

If the UUT design has been completed and finalized, the options at this time are limited. Of course, you can also ask for changes in the next revision or new product, but process improvement always takes some time, and you still have to deal with the current situation.