Question 1

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 2

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 3

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 4

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 5

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

Question 6

What is aluminum boards (MCPCB), and what is its application?

Accepted Answer

Aluminum board(MCPCB) is a unique metal-based copper clad laminate. MCPCB has good thermal conductivity, electrical insulation performance and mechanical processing performance. MCPCB can reduce temperature, improve product power density and reliability, and extend product life.
MCPCB can reduce the volume, the cost of hardware and assembly. MCPCB is a metal circuit board material, which is composed of copper foil, a thermally conductive insulating layer and a metal board. Its structure is divided into three layers, circuit layer, insulating layer, and base layer.
There are three main material numbers for MCPCB, 1050: aluminum with a purity of 99.5%; 5052: Magnesium content is about 2.2~2.8%; 6061: Magnesium content is about 0.8~1.2%. 5052 is commonly used for MCPCB because it has good forming performance, corrosion resistance, and durability.
MCPCB also has the following unique advantages: it meets RoHs requirements; it is more suitable for SMT process.
The main application of MCPCB: often used in high-temperature electrical products or for heat dissipation requirements, such as LEDs, high-power electric lamps, etc., in addition to power supply equipment, audio equipment, automobiles and other applications.
The tests that MCPCB will do are open short and hi-pot tests because the European regulations of lamps and lanterns clearly require that lamps and lanterns have withstand voltage requirements, our company will do 100% of the hi-pot tests.

Question 7

What in the world are the major causes of this PCB bending issue?

Accepted Answer

There are various reasons the cause the PCB bending issue. The most common one is when the stress applied to the PCB is greater than the stress which PCB itself can withstand, the PCB bending issue occurs right immediately.
When PCBs go through the reflow oven for SMT process, the major source stress is the “high temperature”. High temperature will soften the PCBs, plus the factor of Coefficient of Thermal Expansion (CTE) and the characteristic of thermal expansion and contraction of PCB, if the temperature reaches the upper limit of the TG value of the PCBs, than the PCBs will bend.
The PCB designers rarely consider whether there is copper on the PCB edge. On the circumstances of without copper on the PCB edge, the PCB will easily bend while high temperature.
Also if the size of PCB is relatively big and the SMD components are heavy. The PCB bending issue will occur because of the weight.
The V-cut designed for conveniently separating the PCB will also destroy the structure of the PCB, and easily cause the PCB bending issue.

Question 8

What are the differences between ED copper and RA copper in flexible boards (FPC) applications?

Accepted Answer

With more people opt for small electronic devices, it has increased the needs of Flexible boards(FPC) applications for PCB manufacturer. Understanding the differences between ED copper and RA copper, will help PCB designers to choose suitable printed circuit board materials in order to prolong the lifetime of PCB products.

Both ED copper and RA copper are a type of copper foil for flexible boards(FPC). They are a layer of conductive attached to the outer surface of the non-conductive substrate.
During PCB manufacturing process, the ED copper that uses in flexible boards(FPC) is made by using electrolysis method, its crystals tend to grow lengthwise, with long crystal boundaries perpendicular which makes it easy to break. Whereas the RA copper is made by rolling operation, its crystals are smaller and have spherical shapes which give it great extension.
Few tips when choosing the flexible boards(FPC) materials. RA copper has weaker conductivity than ED copper, however, it has much better extensibility, which can reach to 20-45%. RA copper is great for flexible boards(FPC) that needs to bend frequently.
As for PCB products that has less bending requirement, for example: keypads, module boards. The ED copper could be a choice with it great conductivity and lower cost for PCB manufacturers. On the contrary, RA copper will be an excellent choice for bendable boards such as flip phone, Zoom optical lenses.

Question 9

Why are PCBs usually in green color?

Accepted Answer

Solder mask is a protective layer of polymer. It function as a mask layer by forming a protective coating on PCB. The main purpose is for preventing copper trace on PCB from contamination. Furthermore, by covering solder mask on copper trace could prevent broken trace. (Some exposed pads might risk falling out and solder mask could minimize the situation). The solder mask is moisture proof and can provide insulation, resistance, heat endurance and to maintain appearance.
Solder mask, also known as solder resist. Though 99% of PCB use green solder mask, there are other solder mask color available for consideration, such as red, black, blue and so on.
The most common used PCB solder mask is made of Epoxy Liquid. It is typically applied using silkscreen techniques onto the top and bottom side of PCB, where the soldering is not required. In some occasions, the PCB manufacturers might apply inkjet printing technology.
In general, most of PCB manufacturers would apply the lacquer on entire PCB and then put in the oven during pre-baking process and then exposure the film by using contact-exposure technology to transfer the image onto the solder mask layer.
The process of solder mask seems fairly easy. However, if the solder mask is not applied properly during PCB manufacturing process, it might cause some quality issues, such as contamination, skip printing, copper exposure, unequal printing etc. Moreover, the thickness and displacement of solder mask could have affected the quality of tin soldering during SMT.

Question 10

What is the role of holes on printed circuit boards (PCB)? What are PTH / NPTH holes? And what’s the difference between two of them?

Accepted Answer

If you look closely at the printed circuit boards (PCB). You will see that there are many holes with different size on the boards. Those holes on PCB can be simply divided into two types: PTH (Plating Through Hole) and NPTH (Non Plating Through Hole).
The easiest way to distinguish between PTH (Plating Through Hole) and NPTH (Non Plating Through Hole) in PCB is to see if there are any traces of plating on the borehole wall in the PCB.
NPTH (Non Plating Through Hole) refers to a hole without copper in the borehole wall. It is generally used as the positioning hole and screw hole of PCB. The hole diameter is usually larger than PTH.
PTH (Plating Through Hole), the borehole wall has a layer of copper, the PTH holes on PCB has two purposes:
1. Used as component hole for welding DIP components, the hole diameter must be larger than the pin of the component, so that the component can be inserted in the PTH.
2. Another relatively small PTH (Plating Through Hole), also known as “Via”, can be used to connect and conduct wiring between different layers in PCB.

Knowledge