Q: Reliability Test - Accelerated Life Test

Except from E-test and some other Multiple Tests , there is also advanced testing for PCB reliability which is so called Aging Test or Accelerated Life Test. For those application which needs long time working without failure, this kind of testing can help to find out if PCB can withstand abrasion of operation and time. Some certain environment simulation tests can be done to verify the reliability of material by our Programmable Temperature & Humidity Chamber. Here is the test and the testing conditions that we do: High Temperature High Humidity Test Target: To understand influence of moisture absorption to reliability performance of material by environmental simulation. Condition: 85°C / 85% (Temperature / Humidity) Test Time: 168 Hours to 2000 Hours (168 Hours approximately equals 875 Days)

Q: The introduction of Watt MCPCB

The standard aluminum substrate (MCPCB) has a thermal conductivity of about 1~2 W/m.K (also called 1W or 2W), of which you can also find 3W or even higher products. The thermal conductivity of copper or aluminum plate under the dielectric layer is about 400 W/m.K and 200 W/m.K, which is obviously higher than the dielectric layer. The power size of LED in the aluminum substrate is usually marked with "W", such as 1W, 3W, 5W, etc. This refers to the maximum power that LED can withstand, and one important role of the aluminum substrate is to spread the heat to ensure the stable operation of LED. Therefore, when choosing the aluminum substrate, it is necessary to select the corresponding aluminum substrate according to the power range of LED to ensure that the aluminum substrate has sufficient heat dissipation performance. At the meantime, it's necessary to consider the number of layers, line density, size, and the hole size of the aluminum substrate to meet the demand of specific applications. Currently , the power range of aluminum substrate depends on the specific design and manufacturing conditions, including the size, thickness, heat dissipation and layout of aluminum substrate. Generally , the power range of aluminum substrate is between 1W and 10W, but it also depends on the application and design requirements.

Question 1

Why are PCBs designed stack-up?

Accepted Answer

PCB stack-up design is a process of arranging the layer configuration of a multi-layer printed circuit board (PCB). This design considers various factors including electrical performance, signal integrity, EMI (electromagnetic interference), and thermal management. The primary purpose of stack-up design is to maximize the performance and reliability of the PCB.

PCB stack-ups are necessary for several reasons:

Electrical Performance: In high-speed and high-frequency applications, stack-up design ensures stability and consistency in signal transmission. By controlling the distances and arrangements between signal layers, ground planes, and power planes, signal transmission losses and crosstalk can be reduced, thereby enhancing electrical performance.

Signal Integrity: In multi-layer PCBs, couplings and interactions exist between signal layers. Proper stack-up design can mitigate interference between signal layers, improve signal integrity, and reduce signal distortion and jitter.

EMI Suppression: Rational PCB stack-up design can reduce electromagnetic radiation and external interference (EMI) of the PCB. Proper spacing between layers and distribution of copper foils between layers can enhance PCB's EMI suppression capability.

Thermal Management: In high-power applications, stack-up design can aid heat conduction and dissipation. By adding thermal heat spreaders or copper foils at appropriate locations, PCB heat dissipation can be facilitated, preventing overheating and damage.

In summary, stack-up design aims to ensure high performance, reliability, and stability of the PCB while meeting specific requirements of diverse applications. The reasonable stack-up design optimizes PCB's design and performance to the fullest extent.

Question 2

How do PCB Manufacturer Trace Each Production?

Accepted Answer

When client complaint happens, the PCB manufacturer needs to find out the root cause of the problem and prevent it from happening again. However, how to distinguish the defect board from specific production will be essential.
In order to trace each production, the PCB manufacturer will put Date Code and its LOGO on the PCB board. Date code will show when the PCB board is produced. And the manufacturer’s logo will show which PCB manufacturer produces the PCB board. For example, Date code 2316 means the PCB board is produced on the 16th weeks of year 2023. And below “EP AB 94V-0” is the manufacturer’s logo. Once the PCB manufacturer sees its logo and Date code, they could trace the PCB board and start the root cause analysis.

Question 3

Reliability Test - Accelerated Life Test

Accepted Answer

Except from E-test and some other Multiple Tests, there is also advanced testing for PCB reliability which is so called Aging Test or Accelerated Life Test.
For those application which needs long time working without failure, this kind of testing can help to find out if PCB can withstand abrasion of operation and time.
Some certain environment simulation tests can be done to verify the reliability of material by our Programmable Temperature & Humidity Chamber.

Here is the test and the testing conditions that we do:
High Temperature High Humidity Test
Target: To understand influence of moisture absorption to reliability performance of material by environmental simulation.
Condition: 85°C / 85% (Temperature / Humidity)
Test Time: 168 Hours to 2000 Hours (168 Hours approximately equals 875 Days)

Question 4

Why do we not recommend using the PCB which exceeds the shelf life?

Accepted Answer

Why do we not recommend using the PCB which exceeds the shelf life?

Due to the high risk of oxidation and components dropping

Each surface finish has a recommended assembly time and specific storage condition, boards that exceed the storage period will cause oxidation of the surface finish and also the high risk of dropping the components during the high temperature of assembly.

The recommended rework

According to the recommended storage conditions, the manufacturer cannot guarantee their quality if the PCBs have exceeded the storage time. Once the boards exceed the storage time, rework is recommended, such as baking before assembly or reapplying the surface finish, you can check our previous article for more information:
https://www.explus.com.tw/faq/why-does-long-stored-pcb-need-to-be-baked.html

However, not every material is suitable for rework, the binding force of PP between layers will decrease over time. When doing the rework process in the oven, one can run a high risk as those boards past their shelf life can cause delamination and blistering issues.

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Question 5

The packaging methods for Flying Lead, TAB and COF

Accepted Answer

Flex PCB: Also known as a flexible printed circuit board (FPC).

In a previous article, we introduced rolled-annealed copper (RA) and electro-deposited copper (ED).
Today, let's talk about the Flying Lead packaging method.

Flying Lead is a packaging method for flexible boards/high-density flexible boards, which refers to the design and manufacturing method of a connector used to connect PCBs with other devices or systems. It is not specific to a particular type of PCB or packaging method. Therefore, Flying Lead can be applied to various types of PCBs, including rigid PCBs, soft boards, and high-density flexible boards.

There are two common methods for Flying Lead in soft boards (FPC), namely TAB and COF.

TAB (Tape Automated Bonding) is a method that uses a plastic substrate to transfer the conductive circuit onto another substrate and connects the conductive circuit to the chip pins through gold plating. This method requires a longer

The COF (Chip on Film) method involves directly connecting chips to the FPC, requiring shorter flying leads and enabling implementation in smaller spaces. This method requires higher technical requirements and costs, but can achieve higher conductivity and reliability.

Both manufacturing methods have their advantages and disadvantages, so it is crucial to choose the appropriate method based on customer requirements and project needs.

Question 6

What is PCB Panelization Usage Rate? Is There Any Impact on PCB Unit Price?

Accepted Answer

Quality, Cost, and Delivery (QCD)
If you’re responsible for PCB purchasing, what’re the key factors when choosing a PCB supplier. I believe it would be Quality, Cost, and Delivery (QCD). Today we’ll aim on “Cost”.

PCB Panelization Usage Rate Many elements will affect on PCB production cost such as PCB specification, volume of order and so on. Of course, it includes PCB panelization usage rate too. If PCB will be shipped by panel size (sometimes by unit size), the panel design could be either provided from client side or designed by the PCB maker. A relatively high PCB panelization usage rate could cost less for client compared with low PCB panelization usage rate. Every PCB maker has its own standard and guideline when designing PCB panel. Let’s take ExPlus for example.

Click here to know what’s PCB panel size vs. working size.

ExPlus’ Design Guideline of PCB Panelization

The panelization usage rate must be over 85% for 2 layers PCB and 80% for 4 and 6 layers PCB.
The width of breakaway rail must not lower 5mm to avoid potential risk during mounting process.
The added fiducial marks on breakaway rail must ensure 2.5mm between center of fiducial mark and panel outline to avoid any light blocking during assembly process.

Above are only few ExPlus’ guideline when designing PCB panel. The main purpose of PCB panelization is to meet client requirements, fulfill project size characteristics needs, increase activation of mounting process. And the most important of all is to decrease client’s assembly cost.

Question 7

Multiple Testing for PCB before Shipment

Accepted Answer

When it comes to PCB testing, the first idea that comes up must be electric testing.
As being introduced in our previous article, you have already had an idea of how electric testing is conducted.

→ → What is E-TEST? ← ←

However, electric testing is not the only testing we conduct before shipment.
Check below of what we would have done for every batch of PCB shipment.
1. X-Ray check for thickness and substance of surface finish.
2. Size check by our two-dimensional measurer.
3. Microsection for checking copper thickness of PTH and stack up of PCB.
4. Impedance control value measurement to ensure following clients requirement.
5. Solder-ability check to ensure no problem for the coming assembly process.
With every effort that we put to ensure the quality of the PCB, clients can feel safe to entrust us for their PCB jobs.

→ → Testing Equipment of ExPlus ← ←

Question 8

Chamfering V.S. Beveling on PCB

Accepted Answer

PCB_Chamfering_Beveling

In the printed circuit board (PCB) industry, chamfering and beveling are two common techniques used to modify the edges of the board. While the two terms may be used interchangeably in some contexts, they are actually distinct processes with different purposes and outcomes.

Chamfering involves cutting or grinding away a small portion of the edge of the board at a 45-degree angle. This results in a beveled edge that is less sharp and less likely to catch on other materials or objects. Chamfering is often used on the corners of a PCB to prevent damage during handling or installation. It can also be used to create a visual effect, such as giving the board a more polished or finished appearance.

On the other hand, beveling involves cutting or grinding away a larger portion of the edge of the board at an angle other than 45 degrees. This results in a sloped edge that can be used for specific purposes, such as fitting the board into a particular shape or housing. Beveling can also be used to reduce the overall size of the board while maintaining functionality, or to create a more aerodynamic shape for applications such as drone or UAV electronics.

In summary, chamfering and beveling are both edge modification techniques commonly used in the PCB industry. Understanding the difference between these two techniques can help PCB manufacturers choose the most appropriate method for their specific needs.

Question 9

The introduction of Watt MCPCB

Accepted Answer

The standard aluminum substrate (MCPCB) has a thermal conductivity of about 1~2 W/m.K (also called 1W or 2W), of which you can also find 3W or even higher products. The thermal conductivity of copper or aluminum plate under the dielectric layer is about 400 W/m.K and 200 W/m.K, which is obviously higher than the dielectric layer.

The power size of LED in the aluminum substrate is usually marked with "W", such as 1W, 3W, 5W, etc. This refers to the maximum power that LED can withstand, and one important role of the aluminum substrate is to spread the heat to ensure the stable operation of LED. Therefore, when choosing the aluminum substrate, it is necessary to select the corresponding aluminum substrate according to the power range of LED to ensure that the aluminum substrate has sufficient heat dissipation performance. At the meantime, it's necessary to consider the number of layers, line density, size, and the hole size of the aluminum substrate to meet the demand of specific applications.

Currently, the power range of aluminum substrate depends on the specific design and manufacturing conditions, including the size, thickness, heat dissipation and layout of aluminum substrate.

Generally, the power range of aluminum substrate is between 1W and 10W, but it also depends on the application and design requirements.

Question 10

Quality Inspection for Outgoing PCBs

Accepted Answer

Purpose of OQC(Outgoing Quality Check)

After 100% of electric test and appearance check, the PCB manufacturer will conduct “Outgoing Quality Check” to ensure the quality of completed boards meet client’s requirements. Besides compliance with client’s requests, the process of OQC could optimize the production process and improve the quality by detecting the potential quality issue.

Sampling Inspection – MIL-STD-105E Level 2

The PCB manufacturer either follows client’s regulations or control plan to conduct quality inspection. If above not available, then the quality inspection will follow the PCB manufacturer’s standard. The strictness of quality inspection usually could be divided into two categories, automotive products or non-automotive products. Take ExPlus for instance, ExPlus follows MIL-STD-105E Level 2 for both categories. What is “MIL-STD-105E”? MIL-STD-105E stands for military standard 105E which has established for the acceptance or rejection of lots based on the assessment of items attributes. Based on the quantity of taken samples from the lot containing N units, the WHOLE lot is either accepted or rejected. For PCB used in automotive products, ExPlus follows “0 accepted 1 rejected” under MIL-STD-105E Level 2. Which means no matter how many units are inspected, the whole lot will be rejected if there’s one unit not meet the standard. On the other hand, ExPlus follows “MIL-STD-105E Level 2 0.65%” for non-automotive PCB boards. Take 1,000 units for example. Based on the below chart, if there’s only 1 unit not meet the standard within 80 units taken samples, then the whole lot is accepted. Again, sampling inspection is used for outgoing goods inspection after 100% of open circuit/broken circuit and appearance check are performed.

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