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In addition to E-tests and several other tests, there are advanced tests to ensure the reliability of PCBs. This is called aging tests or accelerated life tests. For applications that require long-term operation without failure, this type of testing can confirm whether the PCB can withstand wear from operation and time. Some specific environmental simulation tests can validate the reliability of materials using programmable temperature and humidity chambers. Below are the tests we conducted and the test conditions. High Temperature and High Humidity Test Objective: To understand the impact of moisture absorption on the reliability performance of materials through environmental simulation. Conditions: 85°C/85% (Temperature/Humidity) Test Duration: 168 hours to 2000 hours (168 hours is approximately 875 days)

CCL is mainly divided into three parts: First, high frequency; next, high speed; and third, ordinary. This classification is primarily based on the following three elements: Df dielectric loss: the loss situation of electrical signals within the material; Dk dielectric constant: the delay situation of electrical signals within the material; Tg glass transition temperature: the heat resistance of CCL. The basic criteria are as follows: Df < 0.005: high frequency; Df between 0.005 and 0.01: high speed; Df > 0.01: ordinary (low speed). Higher-grade CCLs have lower Df/Dk values, resulting in less loss and delay, higher technical requirements, and greater added value. As a result, profit margins and unit prices naturally increase. Further classification results in a total of six parts. Automotive applications are classified as high-frequency CCLs due to their relation to safety, along with 5G. High-speed CCLs are used in servers and switches, while ordinary CCLs are generally used in consumer electronics. The main advantages of high-frequency CCLs are: high efficiency, fast speed, good adjustability, and strong durability. In the manufacturing process, resin, catalyst, and curing agent are first mixed and then applied to glass fiber cloth. This is bonded with PP and covered with copper foil to form the so-called copper foil substrate. In terms of cost ratio, CCL accounts for about 67% of the total PCB cost, and this cost ratio is relatively high.

You may have heard about the PCB plug process. Why is epoxy resin used to seal the holes in PCBs? What are its advantages and disadvantages? Improved thermal conductivity: Epoxy filling allows for effective heat dissipation within the PCB, which is beneficial for designs with high-power applications or components that generate significant heat. Enhanced signal integrity: Epoxy filling improves the integrity of high-speed signal transmission, reducing signal loss and electromagnetic interference. It minimizes signal reflection and crosstalk, enhancing overall signal quality. Improved electrical insulation: Epoxy filling enhances the electrical insulation between adjacent layers of the PCB, reducing the risk of shorts and ensuring proper insulation between different signal or power domains. While providing these advantages, epoxy-filled holes also come with several challenges. For example, manufacturing may be more costly compared to non-filled holes, and the process may require additional steps and specialized equipment. Additionally, if rework or repairs are necessary, modifying epoxy-filled holes can be difficult. Therefore, the decision to use epoxy-filled holes should consider the specific requirements and constraints of the PCB design and application.

In previous articles, I discussed "How to Choose PCB Materials," "A Brief Overview of PCB Materials," and "How to Prepare PCB Materials." Today, let's talk about halogen-free FR-4 materials. What is halogen-free FR-4 material? As defined by IPC and IEC, a material can only be considered halogen-free FR-4 if the content of bromine and chlorine is each less than 900 PPM, and the total content of bromine and chlorine is less than 1500 PPM. At the same time, when using halogen-free FR-4, all materials used must meet the halogen-free requirements. Halogen-free FR-4 vs. Lead-free FR-4 The grade of halogen-free FR-4 is higher than that of lead-free FR-4. Halogen-free FR-4 essentially meets the requirements for lead-free assembly. On the other hand, lead-free FR-4 that meets the requirements for lead-free assembly does not necessarily meet the halogen-free requirements. As you know, there are many types of PCB materials. Choosing the right material affects the durability and reliability of the final product.

Regarding wire bonding, ENEPIG can be considered as the initial option. ENEPIG is regarded as one of the most stable surface finishes for wire bonding, but its production cost is significantly higher compared to other surface finishes. Here, there is a solution to use ENIG with an increased gold thickness of 5u" instead of ENEPIG. Below are the conditions and results of tensile tests demonstrating the performance of ENEPIG and ENIG. Test Conditions: Using T1.0 mil gold wire, the tensile strength should be above 3 grams force (in accordance with TM-650 2.4.42.3). PCB A has an ENEPIG finish with Ni: 200u", Pd: 2u", Au: 2u". PCB B has an ENIG finish with Ni: 200u", Au: 5u". Results: PCB A: 5.091 ~ 11.186 (g) PCB B: 4.432 ~ 12.030 (g) In summary, it can be concluded that both ENEPIG and ENIG are suitable for wire bonding.

In the event of a complaint from a customer, the PCB manufacturer must identify the root cause of the problem and take steps to prevent recurrence. However, it is important to have a method to distinguish defective boards from specific production runs. To track each production, the PCB manufacturer affixed a date code and their logo to the PCB substrate. The date code is displayed when the PCB substrate is manufactured. The manufacturer's logo indicates which PCB manufacturer produced the PCB substrate. For example, the date code 2316 indicates that the PCB substrate was manufactured in the 16th week of 2023. Below "EP AB 94 V-0" is the manufacturer's logo. When the PCB manufacturer sees the logo and date code, they can begin root cause analysis by tracking the PCB substrate.

The stack-up design of a PCB (Printed Circuit Board) is the process of planning the arrangement of a substrate consisting of multiple layers. This design takes into account various factors such as electrical performance, signal integrity, EMI (electromagnetic interference), and thermal management. The main objective of stack-up design is to maximize the performance and reliability of the PCB. Here are the main reasons why stack-up design is necessary: - Electrical performance - Signal integrity - Suppression of EMI (electromagnetic interference) - Thermal management In summary, stack-up design is carried out to ensure high performance, reliability, and stability of the printed circuit board, meeting the specific requirements of various applications. Proper stack-up design can optimize the design and performance of the printed circuit board.

The most serious issue with PTH (plated through holes) is the voids that occur in areas where copper plating is required. But do you know why this happens? Common factors lie in the materials, drilling process, or plating process. 1) Materials: The coefficient of thermal expansion (CTE) of the materials may not be suitable for the plating process. Compared to older lead processes, recent lead-free processes have higher requirements for the thermal expansion rate of materials. If the material is still only suitable for lead processes, applying it to lead-free processes may result in voids. 2) Drilling Process: After the drilling process, dust remains on the material. If the vacuum cleaner is not functioning properly and debris accumulates in the holes, the likelihood of voids occurring after plating increases. 3) Plating Process: When the substrate enters the plating solution, bubbles form in the holes. The plating machine vibrates to remove the bubbles, but if the parameters are not accurate or for other reasons, bubbles may remain. And bubbles, just like the residual dust after drilling, can cause voids after the plating process.

Microsection inspection is an important quality analysis method for evaluating interlayer connections and conductor shapes in printed circuit boards (PCBs). This inspection method is typically performed on completed PCBs to ensure that the conductors between each layer meet design requirements and production standards, or to sample and analyze specific locations in case of defects in the product to identify the causes of abnormalities. When conducting microsection inspection, a sample of a specific size is first cut from the completed PCB, and its surface is polished to reveal the internal structure. Then, a microscope is used to observe and photograph the microsection, showing the vias, conductive layers, and dielectric layers of the PCB.

"The number of layers in a PCB" The number of layers in a PCB is determined by the number of copper layers. For example, if the design includes only one copper layer, it is a single-sided PCB. If there are two copper layers, it is a double-sided PCB, and if there are more than two copper layers, it is referred to as a multilayer PCB. Please refer to the diagram below. "Manufacturing Process of Multilayer PCBs" How do PCB manufacturers produce multilayer PCBs? Below, we will explain using a 6-layer substrate as an example. The PCB manufacturer first completes the inner layers and then laminates them with insulating material (prepreg) in between the completed inner layers. Once all layers are correctly positioned, they are pressed together into one. "Double-sided PCB vs. Multilayer PCB" The difference between a double-sided PCB and a multilayer PCB is that a double-sided PCB does not have inner layers and does not require a lamination process. "Single-sided PCB vs. Multilayer PCB" On the other hand, a single-sided PCB does not have inner layers and does not require a PTH (plated through hole) process.

In a previous article, we introduced inner layer processing and pretreatment, but this time we will focus on dry film within that context. Traditional Dry Film Process A photomask is used to transfer the design onto the dry film through exposure. Development processing is carried out to remove the unexposed areas and leave the pattern. Etching or electroplating is performed. Application scene: Suitable for mass production of PCBs with moderate specification requirements.