Q: Precautions for PCB manufacturing in extreme environments

Compared with electronic products used in ordinary environments, electronic products used in extreme environments need to meet higher manufacturing requirements. As the core of electronic products, PCB is extremely important in controlling its performance. PCB materials must be fully considered in PCB manufacturing and layout. As far as extreme environments are concerned, materials that can withstand extremely high temperatures should be selected, such as FR4-008 or PI.These materials can not only withstand extremely high temperatures, but also won't cause the solder mask to detach. Since PCBs that will be used in extreme environments usually have to withstand extremely high heat and temperature fluctuations, the board should be prevented from warping, otherwise it may cut off the circuit, damage the solder joints, and cause problems during the application process. During the PCB assembly process, inspections must be carried out to ensure the quality of the final product. For example, AOI instruments should be used to check the performance of solder joints. The solder paste thickness meter is used to determine whether the solder paste has the best thickness, and whether the thickness is helpful for smooth reflow soldering in the subsequent steps of SMT assembly.

Question 1

Precautions for PCB manufacturing in extreme environments

Accepted Answer

Compared with electronic products used in ordinary environments, electronic products used in extreme environments need to meet higher manufacturing requirements. As the core of electronic products, PCB is extremely important in controlling its performance.

PCB materials must be fully considered in PCB manufacturing and layout. As far as extreme environments are concerned, materials that can withstand extremely high temperatures should be selected, such as FR4-008 or PI.These materials can not only withstand extremely high temperatures, but also won't cause the solder mask to detach.

Since PCBs that will be used in extreme environments usually have to withstand extremely high heat and temperature fluctuations, the board should be prevented from warping, otherwise it may cut off the circuit, damage the solder joints, and cause problems during the application process.

During the PCB assembly process, inspections must be carried out to ensure the quality of the final product. For example, AOI instruments should be used to check the performance of solder joints. The solder paste thickness meter is used to determine whether the solder paste has the best thickness, and whether the thickness is helpful for smooth reflow soldering in the subsequent steps of SMT assembly.

Question 2

PCB applies in smartwatch (Wearable devices)

Accepted Answer

Common smartwatches include Apple Watch/Garmin/Xiaomi bracelet (ExPlus also makes related wearable devices! Bluetooth headsets/police equipment, etc.)

Wearable devices have the characteristics of light weight in appearance, and the product itself also has the four major characteristics of integration, lightness and softness, wireless, and universal use. In order to meet the electrical requirements of wearable devices, it is necessary to use SiP chip carrier boards and 3D IC chips. High-end PCB technology such as carrier board, hard board with embedded active/passive components, high bending resistance FPC and Low Dk & Df PCB materials.

The wearable application industry is divided into five categories: Healthcare and Medical, Fitness and Wellness, Infotainment, Industrial and Military.

To put PCB in the smartwatch, and due to the small space, fewer components, and less memory configuration, most of the designs are designed with a flexible board or a combination of rigid and flexible boards.

Nowadays, wearing a smartwatch is like having a personal digital assistant. The functions that can be processed are: camera, thermometer, compass; GPS; heart rate monitoring, diving computer, etc.

Question 3

What is HiPot Test?

Accepted Answer

HiPot test, also called insulation withstand voltage test, is a non-destructive reliability test that can measure the "breakdown voltage" and "insulation resistance" of PCB products. High voltage will be applied to PCB products within a certain period of time, usually 1.5KV~3.0KV (daily power consumption is 110V or 220V several times the voltage, the conditions and standards vary depending on the product) to test the electrical safety of PCB products whether the characteristics and insulation performance are qualified, under high voltage, some materials with poor insulation will be broken down and a short circuit will appear.

The HiPot test is carried out by allowing the input power terminal of the PCB product to withstand a high voltage for a limited period of time, and measuring its collapse state. This test stipulates that the PCB "Does not allow arc breakdown or collapse during the period when a high voltage is applied.

The HiPot test can also detect potential defects in PCB products, such as:
1) The insulating effect of the insulating material is not good
2) There are pinholes on the insulator
3) Insufficient electrical clearance between components
4) The insulator is squeezed and broken

Question 4

What is the bonding on the PCB?

Accepted Answer

Bonding, that is, chip bonding, chip coating. Bonding is a wire bonding method in the chip production process. It is generally used to connect the internal circuit of the chip to the package pins with gold wires before packaging.

What will be done after bonding (after the circuit is connected to the pin)?
The chip is packaged with glue, and use the packaging technology, COB (Chip On Board). The tested wafer is implanted on a special circuit board, and then the wafer circuit is connected to the circuit board with a gold wire, then after melting, the organic material with special protective function is covered on the wafer to complete the later packaging of the chip.

What are the advantages of Bonding?

The bonding chip is anti-corrosion, anti-vibration, and stable performance:
The advantage of this packaging method is that the stability of the finished product is better than that of the traditional SMT patch method. Because the circuit board is affected by moisture, natural and human, it is prone to short circuit and open circuit. The bonding chip is protected by organic materials, and isolated from the outside, there is no moisture, static electricity, and corrosion.
Bonding wafers are suitable for mass production: The product has strong consistency and long service life. This packaging technology has the advantages of low cost, space saving, light weight, good heat dissipation, and simple packaging method.
Application of bonding:
Many of the LCD screens of mobile phones, PDAs, MP3 players, digital cameras, and game consoles will use bonding.

Question 5

What’re the pro and con with OSP surface finished

Accepted Answer

The OSP is kind of PCB surface finish that complies with RoHS certification.
The OSP is a chemical substance to cover the PCB surface with a layer of protective film on the copper surface.
The features of the OSP are anti-oxidation, heat-resistance and moisture-resistance. It can prevent PCB surface from copper oxidation effectively.
The advantages of PCB surface finish that applies with OSP are easy process, flat surface, eco-friendly and lower cost.
The disadvantages of PCB surface finish that applies with OSP are having shorter shelf life and easier to be scratched.

Question 6

What is ENIG (Immersion Gold)?

Accepted Answer

Before introducing immersion gold, we would like to talk about ''surface finish'',.

Surface finish is the "small movements" made on the surface during various metal processing. It is easier to understand the way of painting and covering other materials. An iron railing painted with paint is one of the practical applications of surface finish.

"Immersion Gold" means "nickel immersion gold", which is one of the surface finish for PCB. Immersion gold is cheaper than gold plated, so the shiny part of electronic parts is usually immersion gold. A thin layer of gold prevents oxidation of copper.

The characteristic of immersion gold is that it can attach "nickel" and "gold" to the copper sheet without cumbersome electroplating, and it is much smoother than gold plated. It is very important for the development of smaller and smaller electronic parts and parts that require high flatness.

Question 7

IPC Standard

Accepted Answer

Generally, the industry is divided into three categories with IPC as the standard, among which Class 2 is the standard.
Class1 consumer products, general electronic products and electronic peripherals
Class2 high-performance electronic products, communication equipment, commercial equipment
Class3 high reliability products, military applications

If the customer has no specific requirements, ExPlus follows Class2, IPC-6012 as the standard to ensure the quality of its materials.
High-quality PCB needs to meet:

In addition to the trace width, thickness, and spacing of the high-quality PCB should meet customer requirements to avoid trace heating, open and short circuit. The copper on the outer layer of the PCB must not be easy to fall off and oxidize, otherwise the PCB will be damaged soon after oxidation.
The PCB should not be easily deformed to avoid deformation of the PCB shell and misalignment of the screw holes after installation. Now it is installed mechanically, and the position of the PCB hole and line error and position should be within the allowable range.
The PCB should consider the high temperature, high humidity or other special environment required by the customer without additional electromagnetic radiation. The surface performance of the PCB should meet the subsequent installation requirements.

Generally speaking, a small volume of PCBs will use flying probe testing due to cost considerations, while mass-produced PCBs use fixtures to detect open and short circuits. In addition, visual inspection of PCB appearance, characters, solder mask, bevel, hole break, V-CUT, etc. are also necessary procedures before shipment.

Question 8

What is HASL on the PCB?

Accepted Answer

HASL boards, Hot Air Solder Leveling, is to spray a layer of tin on the surface of the copper foil to protect the copper foil, and then use hot air to form an air knife to level the tin surface. There are two common spray Tin equipment, vertical and horizontal.
HASL used to dominate the PCB surface treatment process, which is an excellent process for larger components and wires with larger spacing.
However, the industry is gradually reducing the use of HASL because it is relatively dirty, unpleasant and dangerous in the process. The trend of lead-free has begun in recent years, which has further restricted the use of HASL. Although there is a so-called lead-free HASL, it involves issues such as equipment compatibility.
Advantages of HASL:
1. Because the plating layer itself is tin, a better Wetting effect can be obtained.
2. HASL is also low in price and good in welding performance, usually only for the first side, not necessarily for the second reflow side.
3. Long storage time and mature technology; suitable for visual inspection and electrical measurement.
Disadvantages of HASL:
1. Not suitable for welding fine gap pitch and too small parts because the surface flatness of HASL is not good.
2. It is easy to have solder bead in PCBA process, and it is easy to cause short circuit to fine pitch parts.
3. When used in the double-sided SMT process, since the second side has passed the first high-temperature reflow soldering baptism, it is very easy to spray tin and re-melt to produce tin beads or similar droplets that are affected by gravity and drop into spherical tin spots. In addition, the second reflow surface may also cause tin oxidation and IMC generation in advance to affect solderability during the first reflow.

Question 9

HDI Board and Its Applications

Accepted Answer

The definition of HDI: The American IPC-2315 standard considers that the minimum conductor width and spacing of the design are ≤0.10 mm, the (mechanical or laser) through hole diameter is ≤0.15 mm, and there are buried and/or blind holes between layers, is called HDI board.
HDI boards are generally manufactured by layer-by-layer method, the more the number of layers, the higher the technical grade of the board. Ordinary HDI boards are basically one-time build-up. High level HDI uses two-time or more build-up technology. At the same time, advanced PCB technologies such as stacking holes, electroplating hole filling, and laser drilling are used.
When the PCB increases to more than eight layers, and manufactured with HDI, its cost will be lower than that of the traditional and complex laminated process. HDI board is conducive to the use of advanced packaging technology, and its electrical performance and signal accuracy are higher than traditional PCB. In addition, HDI boards have better improvements in radio frequency interference, electromagnetic wave interference, electrostatic discharge, and heat conduction.
Features of HDI board:
1. Increase the wiring area and the line density
2. Reduce the thickness of the insulating medium, and the thickness and weight of the board
3. Shorten the wire interconnection length, reduce electrical signal interference and loss
4. The thickness of the via hole is relatively small, which improves the interconnection reliability
5. The structure design of the via hole is convenient, the design freedom is large, and the design efficiency is improved
The main application of HDI board is that HDI started with the development of mobile phones, and expanded the market and improved performance as feature phones were transformed into smart phones. HDI boards are now used in electronic devices outside of mobile phones, such as notebook computers and tablet computers, automotive electronics, aerospace, medical devices and wearable electronic devices, robots and smart devices.

Question 10

What are the purpose and application of rigid-flex PCB?

Accepted Answer

Rigid-flex PCB is a special flexible PCB composed of rigid PCB and flexible PCB laminated together, with a compact structure, and metalized holes to form electrical connections. It has the characteristics of high density, thin traces, small aperture, small size, light weight, and high reliability. It is still stable under vibration, impact, and humid environments.
Rigid-flex PCB has a bendable and three-dimensional installation, which effective use of installation space, is widely used in mobile phones, digital cameras, digital video cameras and other portable digital products.
Advantages of rigid-flex PCB,
1. Save the process of using connectors or soldering Hot Bar.
2. Shorten the signal transmission distance of the rigid-flex PCB and the speed is increased, which can effectively improve the reliability.
3. Simplify product assembly and save assembly working hours.
Disadvantages of rigid-flex PCB,
1. In terms of the unit price of “rigid-flex PCB” will be more expensive than “flexible board + rigid board”, but if adding the price of the connector or the cost of hot bar soldering, Prices may tend to be consistent.
2. SMT and reflow oven may need carriers to hold the flex PCB, which increases the SMT assembly cost.

What are the purpose and application of rigid-flex PCB

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