Archive for the ‘SMT Technology’ Category

Understanding Counterbore and Countersunk Holes in PCB Design

Saturday, July 8th, 2023

When we talking about the holes in PCBs (Printed Circuit Boards), may somebody always curious about two special holes: Counterbore hole and Countersunk hole. They are easy to be confused and easy to misunderstanding if you are a layman of PCB. Today, we will introduce the differences between counterbore and countersunk for details, let’s keep reading!

What is a Counterbore Hole?

A counterbore hole is a cylindrical recess on a PCB that has a larger diameter at the top surface and a smaller diameter at the bottom. The purpose of a counterbore hole is to create space for a screw head or a bolt’s flange, allowing it to sit flush with or slightly below the PCB surface. The larger diameter at the top accommodates the head or flange, while the smaller diameter ensures that the fastener’s shaft or body fits snugly.

What is a Countersunk Hole?

On the other hand, a countersunk hole is a conical recess on a PCB that allows the head of a screw or bolt to sit flush with the PCB surface. The shape of a countersunk hole matches the profile of the fastener’s head, creating a seamless and level surface when the screw or bolt is fully inserted. Countersunk holes typically have an angled side, often 82 or 90 degrees, which determines the shape and size of the fastener head that will fit into the recess.

Counterbore VS Countersunk: Geometry

While both counterbore and countersunk holes serve the purpose of accommodating fasteners, their main difference lies in their geometry and the types of fasteners they accommodate.

Counterbore holes have a cylindrical recess with two different diameters, while countersunk holes have a conical recess with a single diameter.

Counterbore holes create a stepped or raised region on the PCB surface, whereas countersunk holes result in a flush or recessed surface.

Counterbore VS Countersunk: Fastener Types

Counterbore holes are primarily used for fasteners with a head or flange, such as bolts or screws that require a solid mounting surface.

Countersunk holes are designed for fasteners with a conical head, such as flathead screws or countersunk bolts, to achieve a flush surface.

Counterbore VS Countersunk: Drill angles

Different sizes and drilling angles of drill bits are offered for producing countersinks, depending on the intended use. These angles can include 120°, 110°, 100°, 90°, 82°, and 60°. However, the most frequently employed drilling angles for countersinking are 82° and 90°. For optimal outcomes, it is essential to align the countersink angle with the tapered angle on the underside of the fastener head. On the other hand, counterbore holes feature parallel sides and do not necessitate tapering.

Counterbore VS Countersunk: Applications

The choice between counterbore and countersunk holes depends on the specific requirements of the PCB design and the components being used.

Counterbore holes find applications in situations where a secure and flush fastening of components or mounting plates is necessary. They are commonly used to fasten connectors, brackets, or PCBs to an enclosure or chassis.

Countersunk holes are often employed when aesthetic considerations are important, as they provide a sleek and level surface. They are frequently used for mounting PCBs to surfaces where a flush finish is desired, such as in consumer electronics or decorative applications.

Counterbore and countersunk holes are important features in PCB design, enabling efficient component mounting and secure fastening. Understanding the differences between these two types of holes allows designers to select the appropriate option based on the specific requirements of their circuit board applications. Whether it’s ensuring a secure connection or achieving a visually pleasing finish, the choice between counterbore and countersunk holes plays a crucial role in the overall functionality and aesthetics of a PCB assembly.

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5 Tips Tell You How to Solder BGA Better in PCBA

Monday, May 29th, 2023

BGA (Ball Grid Array) soldering is a widely used method in the electronics manufacturing industry for mounting integrated circuits onto printed circuit boards (PCBs). This method provides a more compact and reliable connection compared to traditional through-hole or surface mount technology (SMT). However, the complexity of BGA soldering poses various obstacles during the manufacturing process. Herein, we will explore the challenges faced in BGA soldering and discuss effective strategies to address them.

What is BGA Soldering?

BGA soldering is a technique that involves the attachment of integrated circuit packages to a PCB using an array of solder balls. These solder balls are typically made of lead-based or lead-free alloys, depending on environmental regulations and specific requirements. The BGA package consists of a substrate, which acts as a carrier for the integrated circuit, and the solder balls that form the electrical and mechanical connections between the package and the PCB.

(BGA_balls)

The Importance of BGA Soldering in Electronics Manufacturing

BGA soldering plays a critical role in the manufacturing of various electronic devices such as computers, smartphones, and gaming consoles. The increased demand for smaller and more powerful electronics has driven the adoption of BGA packages. Their compact size and high pin density make them suitable for advanced applications where space is limited.

Challenges Faced in BGA Soldering

  • Component Alignment and Placement

One of the primary challenges in BGA soldering is ensuring accurate component alignment and placement on the PCB. The small size of the solder balls and the dense layout of the BGA package make it difficult to achieve precise positioning. Misalignment during the assembly process can result in solder bridges, open connections, or mechanical stress on the package.

To address this challenge, manufacturers employ advanced technologies such as Automated Optical Inspection (AOI) and X-ray Inspection. AOI systems use cameras and image processing algorithms to verify the correct alignment and placement of BGA components. X-ray inspection, on the other hand, allows manufacturers to see beneath the surface of the PCB and detect any misalignment or defects that may not be visible to the naked eye.

(Alignment)
  • Solder Paste Application

Another significant challenge in BGA soldering is achieving precise and consistent solder paste application. Solder paste, a mixture of solder alloy and flux, is applied to the PCB pads before placing the BGA package. Inadequate or excessive solder paste can lead to solder defects such as insufficient solder joints, solder voids, or solder bridging.

To overcome this challenge, careful attention must be given to stencil design and aperture selection. Stencils with appropriate thickness and properly sized apertures ensure accurate solder paste deposition. Additionally, manufacturers can employ Solder Paste Inspection (SPI) systems to verify the quality and consistency of the solder paste applied. The solder paste that Best Technology uses is SAC305 solder paste, which has good printability and excellent stability.

(SAC305_Solder_paste)
  • Temperature Profiling

Temperature profiling, or we can say the thermal management, it is crucial in BGA soldering to ensure proper reflow of the solder paste. The reflow process involves subjecting the PCB to a carefully controlled temperature profile, allowing the solder paste to melt, form a reliable joint, and solidify. Inadequate temperature profiling can lead to insufficient solder wetting, incomplete reflow, or thermal damage to components.

Manufacturers must optimize the reflow oven setup and calibration to achieve the correct temperature profile. Thermal profiling techniques, such as the use of thermocouples and data loggers, help monitor and control the temperature during the reflow process.

  • Reflow Process

The reflow process itself presents challenges in BGA soldering. The soak zone, ramp rates, and peak temperature must be carefully controlled to prevent thermal stress on the components and ensure proper solder reflow. Inadequate temperature control or improper ramp rates can result in solder defects such as tombstoning, component warpage, or voids in the solder joints.

Manufacturers need to consider the specific requirements of the BGA package and follow recommended reflow profiles provided by component suppliers. Proper cooling after reflow is also essential to prevent thermal shock and ensure the stability of the solder joints.

(BGA_reflow)
  • Inspection and Quality Control

Inspection and quality control are critical aspects of BGA soldering to ensure the reliability and performance of the solder joints. Automated Optical Inspection (AOI) systems and X-ray inspection are commonly used to detect defects such as misalignment, insufficient solder wetting, solder bridging, or voids in the solder joints.

(AOI)

In addition to visual inspection techniques, some manufacturers may perform cross-section analysis, where a sample solder joint is cut and examined under a microscope. This analysis provides valuable information about the quality of the solder joint, such as solder wetting, void formation, or the presence of intermetallic compounds.

In a word, BGA soldering presents unique challenges in electronics manufacturing, primarily related to various factors. By addressing these challenges effectively, manufacturers can ensure the reliability and performance of BGA solder joints, contributing to the production of high-quality electronic devices. Best Technology has rich experience in PCBA assembly and we mounted thousands PCBs for our customers, whatever it is simple design or complex design, all the products are assemble perfect and work well in customer side. Please feel free to contact us for any questions about PCBA.

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Why Consider Even-Number Multi-Layer PCBs For Your Project?

Tuesday, March 7th, 2023

With the great demands about high-tech electronic equipment, although the single sided PCB or double-sided printed circuit boards have their advantages, multi-layer designs are more beneficial for some applications, that’s why the more and more popular and wide usage of multi-layer PCBs.

(Multilayer_PCB)

Currently in the market and electronic industry, almost of the multi-layer PCB have an even number of layers such as 8, 10 or 12 layers, why designers didn’t consider an odd-number layers? Today let’s explore the reasons together.

  • Higher cost spent

Normally the standard layers of a multi-layer PCB in the industry are even-numbers, and as the manufacturing technology becomes more and more mature, the cost of fabricating a multi-layer PCB is relative competitive.

But if you want to produce odd-numbers PCB, may the odd-number layers save the cost of material for one layer but the processing cost increase significantly to an even-numbers. Because the core structure requirement for odd layered PCB increases the production cost greatly. However, an even layered PCB can save these costs and reduce the overall manufacturing cost, so why not consider the even number layers?

  • Long lead time

Long delivery time is unescapable because of the immature fabricating technology. In particular with the odd-layer, the stack up will be unbalance. For example, if it’s an odd layered circuitry, due to the standard symmetrical requirement, the layers will be separated to 2 layers in a one side and another side is 3 layers, so one of the copper layers will be etched away and the odd layered PCB may create uneven weight during the copper plating stage and result in irregular plating issues. This non-standard, odd-layered stack requires an extra core process for layer bonding and adds to the manufacturing time and cost. So, it’s always recommended to use an even number of layers in the PCB stack-up.

  • Potential quality issue

Quality is very important and crucial for end-application, and the best reason of why not design an odd-number multi-layer PCB is the odd-number layers PCB is very easy to get twist due to the unbalance copper layers. When the PCB is cooled after the multi-layer circuit bonding process, the different lamination tension between the core structure and the foil structure can cause the PCB to bend when cooled. As the board thickness increases, the risk of bending becomes greater for composite PCBs with two different structures.  The key to eliminate circuit board bending is to use balanced layering.  Although PCBs with a certain degree of bending meet the specification requirements, subsequent processing efficiency will be reduced, resulting in increased costs. Because assembly requires special equipment and technology, the accuracy of component placement is reduced, so the quality will be damaged.

In addition, the twist of an even-number layers PCB can be controlled below 0.7% (IPC 600 standard), but odd layers unable to reach to this quality standard. What’s more, when the warpage of a circuit board greater than 0.7% will seriously affect the operation of Surface Mounted Technology (SMT) process and the reliability of the whole product. Therefore, the designers do not design odd layer generally, even if the odd layer enables to achieve the function, will be designed into false even layer, that is, 5 layers designed into 6 layers, 7 layers designed into 8 layers of board.

Anyway, more layers it is, more complex & difficult the manufacturing will be, and more expensive the cost will be, and the lead time of multi-layer PCB also is different from normal one. So you must choose a right supplier who can provide One-stop service include designing, evaluating, manufacturing or even repairing. Best Technology is an expert in the production of multi-layer PCBs for many companies around the world for over 16 years. Contact us right now and send us inquiries, we are so confident that we can be one of your most reliable suppliers in China.

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The Difference Between 2L MCPCB and Double Sided MCPCB

Monday, February 27th, 2023

In our last article, we know what a metal core PCB is, in this post, we will introduce what is the difference between 2L MCPCB and Double sided MCPCB. Please continue to read if you want to know more about metal core printed circuit board.

Today we will explain from these four contents as following:

  1. Stack up (structure)
  2. Heat dissipation
  3. SMD populate
  4. Manufacturing technology

Stack up of 2L MCPCB and Double Sided MCPCB

For a 2L MCPCB, the metal core is positioning on the bottom side of the MCPCB as a cooling carrier to the whole MCPCB, while the metal base of double sided MCPCB is located in the middle of two copper trace. In generally, some PTH (plated-through-hole) vias are needed to designed to connect the bottom and top traces.

Below are the stack ups of these two kinds of products, from the structure, we can easily distinguish which one is 2L MCPCB and which one is double sided MCPCB.

Heat dissipation of 2L MCPCB and Double Sided MCPCB

Due to the different structure of the two products, their heat dissipation performance is also different. The main reason is the heating of double-sided metal core circuits can be spread out through both top and bottom side, while the heating generate by SMD components of 2 layers circuit only can be dissipated through bottom (metal) side and the heat need to go down layer by layer. In addition to this, the dissipation of FR4 is not good than metal materials, so double-sided metal core printed circuits perform better heat dissipation performance than 2 layers MCPCB.

Surface mounted locations (SMD populate)

Nowadays, surface mounted technology (SMT) is widely used in printed circuit board industry, more and more designers prefer to populate electronic components of the circuit surface to achieve high density, stable electrical performance and high reliability. 2L metal core circuit boards and double-sided metal core circuits also show their different mounted locations in this aspect.

The populate location of a 2L MCPCB only available on copper trace side, that is top side. And a double-sided metal core PCB can mount components on both top and bottom side, because both of them exist copper trace on it.

Manufacturing technology

May somebody will curious about “Are these two products produced in the same process/technology?”

The answer is obvious “NO, they have a different laminate process when fabricating.”

Different with single layer MCPCB, double sided MCPCB requires an additional pressing step to laminate the thermal conductive layer and metal core together. But sometimes, some raw Metal Clad material vendor will supply board material which already laminated.

For 2 layers metal core PCB, due to it is made of a single MCPCB and a double-sided FR4 PCB, the first thing we should make a double sided FR4 PCB, then laminate the PCB together with the single MCPCB. But due to the thermal conductive layer (pure adhesive) is easy to overflow during laminating process, which will cause the poor adhesion and crack between metal core and FR4 PCB. In the meantime, to avoid such problem, an experienced operator is needed to proceed the laminated process. That is why the lead time and cost of a 2 layers metal core circuit is much longer and expensive.

This is the end of this post, if you still have some questions or difficulties about the metal core PCB, welcome to contact us at sales@bestpcbs.com, our professional sales team and engineering team will give you a best solution for free.

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How to choose surface finish on Printed Circuit Board?

Saturday, December 17th, 2022

When finish the PCB design, we should choose a suitable surface finish to protect traces from corrosion. Nowadays, the most popular surface treatments for PCB manufacturer to use are HASL/LF HASL, OSP and ENIG.

Different surface treatment has its unique functionality and the cost also is different. This article we will show you the pros and cons of the three surface finishing which use while the PCB manufacturing process.

HASL Surface Finish

HASL (Hot Air Solder Level) can be known as tin-lead HASL and lead-free HASL, it was the mainstream surface treatment technology in the 1980s, but with the increased of “small and high density” demands in PCB, there are less and less circuit boards use the HASL technology because it will cause the defective products due to the solder point are easy to leave on the board surface during SMT process. In view of this situation, some PCB board manufacturers or designers prefer use OSP or immersion gold to ensure the good quality products as well as smooth production process.

  • Tin-lead HASL

Advantages:

1) Economical and widely available.

2) Excellent solderability.

3)Better mechanical strength & lustrousness than lead-free HSAL.

Disadvantages: it is harmful to environment and violates RoHS compliance.

  • Lead-free HASL

Advantages: low cost, good solder performance and environmental.

Disadvantages: mechanical strength & lustrousness are not good than lead HASL.

In additional, due to the poor surface flatness of HASL circuit boards, neither leaded nor lead-free HASL is not suitable for soldering fine-pitch components or plated through-holes, because it will cause the short circuits and poor welding during the assembly process.

(LF_HASL)

OSP

OSP (Organic Solderability Preservatives) also named as pre flux, the working principle is to generate a layer of organic film chemically on the copper surface to protect the surface from oxidation or vulcanization in the room environment. Meanwhile, OSP also can increase the oxidation resistance, heat shock resistance and moisture resistance of a PCB. 

OSP is equivalent to an anti-oxidation treatment, the protective thin film can be easily removed by the flux quickly under the high soldering temperature, then it makes the exposed copper surface immediately combined with the molten solder in a very short time to become a solid solder spot.

At present, the usage of OSP surface finishing process has increased significantly because it is appropriated for both low and high-end products. If your application has no surface connection functional requirements or storage life limitations, the OSP process is the most desirable surface treatment process.

(OSP_surface_treatment)

Advantage:

1)With all the advantages of bare copper soldering, expired (more than 3 months) boards can also be resurfaced, but one time is better.

2)Good for fine-pitch, BGA and smaller components.

3)Low cost and easy to rework.

4)Simple process and easy to ensure quality.

Disadvantage:

1)OSP is easily affected by acid and humidity, so must be packed with vacuum.

2)Need to do surface treatment again if storage time more than 3 months.

3)It should be used within 24 hours after unpacking.

4)OSP is an insulating layer, so the test point must be printed with solder paste to remove the original OSP layer for electrical testing.

ENIG

ENIG (Electroless Nickel/Immersion Gold) is one of a chemical nickel gold deposition method, the working principle is to generate a layer of coating by chemical REDOX reaction to get a thicker gold layer. Currently, ENIG is mainly used in the surface of the circuit board with connection functional requirements and long storage life.

Advantage:

1)Can be stored long time as well as no oxidation.

2)Good flatness surface and suitable for small solder point components.

3)Good solderability.

4)Can be used as the base material for COB wire bonding.

Disadvantage:

1)High cost than other two surface treatments.

2)Easy to exist black-pad issue during production process.

(ENIG)

As we can know from above information, each PCB surface treatment has its own merit and demerit, you can choose the one according to the effect you want to reach, as well as your cost. 

If you don’t know which is best for you, you can send inquiry to us, our professional engineering team and PCB sales will choose the suitable one for you. Welcome to contact us if you have any other questions.

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Why Printed Circuit Boards are Important for Electronics?

Wednesday, December 7th, 2022

Printed Circuit Boards are the core of the electronics devices, and they exist in everywhere and be everything from your electronic equipment such as mobile phone, computers, so what are they? Let’s explore the secrets together and know why they become more common as technology advances.

What are Printed Circuit Boards?

A printed circuit board also known as PCB for short, is an electronic board for connecting metal circuits by mounting different electronic components in a device and have it do its functions.

PCB is made of fiberglass and laminate materials or a composite epoxy with conductive, it can be made to varies shapes and sizes depends on what applications it will be used for—some have many holes on it while some only have several pads or traces.

In most of devices, we can see there are many components or wires mounted or connected on the surface of PCB, which comes into two different pathways –surface mount and through-hole. Surface mount is a technology that can be abbreviated as SMT, it is a famous technical that mount electronic components (typically SMDs) attached on top of a pad by melted solder paste. Through-hole generally refers to components that have wires through the plated-through-holes that drilled into the circuit board. Both ways are commonly use, but currently with the fast development of the technology advance, surface mount is more popular than through-hole as it is more convenient for production.

What the Functions of Printed Circuit Boards?

The main functions of a PCB is to connect different components and achieve a communication between components and devices, that can be used for everywhere you can think of – Computer, phones, televisions, tablets, cameras, projectors, and so on….

For a simple example, a phone has a PCB that can connect screen, the buttons, cameras, and the circuits on the both sides. Without this board, those components wouldn’t be able to transmit signals and talk to each other and the phone would cease to function.

In addition, electronic equipment using printed board enable to avoid the error of manual wiring, and can realize the automatic insertion or installation of electronic components, automatic soldering, automatic detection by communicate with each other, to ensure the quality of electronic products, improve labor productivity, protect components from damaged, reduce costs, and easy to maintenance.

The advantages of Printed Circuit Boards

PCB performs a number of advantages in electronic industries, a most significant feature is they make products be smaller and more portable as its density circuits and components communication. The density circuits on PCB allows it take up much space for components so you can get a smaller product.

  • High density

Over the past decades, the high density of printed boards has been developed with the improvement of integrated circuits and the advancement of installation technology.

  • High reliability

Through a series of checks, tests and aging tests, the PCB can be guaranteed to work reliably for a long time (generally 20 years).

  • Designability

For various performance (electrical, physical, chemical, mechanical, etc.) requirements, can PCB be achieved to such requirements in short time and high efficiency according to design standard rules.

  • Maintainability

By means of standard PCB design rules, once the program or device failure, users fix the devices quickly.

  • Cooling abilities

Overheating is one of the biggest reasons of electronics failure, so by keeping them cool with a PCB, you can increase the lifetime of your product.

Types of Printed Circuit Boards

Best Technology provides different kinds of PCBs and PCBAs for our customers, for a quickly reviewing, we listing as below:

  • Rigid Printed Circuit Board (FR4-PCB)
  • Flex Printed Circuit Board (FPCB)
  • Rigid-Flex PCB
  • Metal Core Printed Circuit Board (MCPCB)
  • Ceramic Board
  • SinkPAD Board
  • Other special PCB such as heavy copper PCB, HDI PCB, RF PCB, and so forth
  • PCB assembly

In a word, with the development of electronics, it’s necessary to have a functional part like the PCB that can keep up with the demand. Next step, contact us if you have PCB demands.

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Differences Between Solder Mask and Solder Paste in PCB

Wednesday, December 7th, 2022

When it comes to solder mask and solder paste, there are some engineers confused about their functionalities and even most of laymen thought they are the same, this is not hypothetical, it is real that happened to me. So today let’s explain differences between Solder Mask and Solder Paste for you.

Part 1: What is Solder Mask?

If you had ever seen a printed circuit board, you may see there is a layer of green ink cover on the PCB surface while some orange-yellow areas didn’t cover by ink. In PCB industry, the green ink we called Solder Mask, or abbreviated as S/M, and exposed area is copper, they were leave as GND plane or soldering pads to mount electronic components.

Solder mask is a liquid acrylic oligomer, which has variety of colors such as red, blue, green, white, black. Green is commonly used in the process of PCB manufacturing, so some professional engineers call it as green oil.

Solder_mask

Solder mask applied on the PCB designed as a protection layer to avoid oxidation, corrosion and other environmental impacts when they leave production line. In addition, solder mask between solder pads also can help to prevent forming to solder bridge when assembly.

Below are some other functions of coating a layer solder mask:

  • Prevent physical line breaking of copper trace
  • Only weld in the area that must be soldered to avoid waste of soldering
  • Reduce copper pollution to soldering groove 
  • Prevent insulation deterioration and corrosion caused by dust, moisture and other external environmental factors 
  • With high insulation, so that the high-density circuit is possible

Part 2: What is Solder Paste?

Solder Paste also known as “Solder cream”, is a most important soldering material used in surface mount technology (SMT) process. Mainly function for soldering resistors, capacitors, ICs and other electronic components onto the PCB surface to form a permanent connection.

The solder particles are a mixture of solder formed by mixing solder powder, flux and other surfactants and thixotropic. Traditionally this used to be tin and lead, but with the legislation has been introduced around the world, to only use lead free solders. These may be made from a variety of mixtures, Best Technology commonly used is SAC305 which includes 96.5% tin, 0.5% copper and 3.0% silver, some manufacturers also use 99.7% tin and 0.3% copper, whereas there are other mixtures that include other metals including tin.

Due to the role of solder paste in assembly, solder paste storage is extremely important. However, solder paste got into drying during storing became a common problem faced by most PCBA manufacturers, so How to solve solder paste dry problem is premier.

Solder_paste

Part 3: The Difference Between Solder Mask and Solder Paste

  1. Solder mask is a formal part of PCB, but solder paste ONLY for PCB assembly.
  2. Solder mask is not allowed on the solder pads while solder paste can be printed on the solder pads openings.
  3. Solder mask is used for applying solder mask ink, but solder paste is used for applying paste.
  4. Solder mask has many available colors, but paste mask visually gray.
  5. Solder mask is coating during PCB fabrication, but solder paste is printing when PCB assembly.

With over 16 years in PCB industry, Best Technology is one of the most reliable PCB and PCBA supplier in Asia, we commit to provide high quality products with excellent service before and after sales, to take care our customers wholeheartedly, and to treat customers’ business as ours. At the same time, we keep learning and continually to improve ourselves so that we can catch up the latest technology trend and provide better and better service for our customers.

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Why Solder Paste became Dry and How to Solve This Problem

Thursday, August 18th, 2022

As a One-stop PCBA manufacturer, I believe most of manufacturers have faced a problem of solder paste became dry during SMT process, especially in hot summer, and there will be a large number of defects come out when solder paste was dry, such as poor printing, false solder, components be shifted, cold solder and so on, which will greatly decrease assembly efficiency and PCBA quality.

Do you know why the solder paste became dry?

A serious dried solder paste
Good solder paste

After checking and discussing with our SMT engineers, we found the root cause of solder paste be dry is corrosion, in below images you can see the detailed solder powder morphology of corrosion.

2-a Solder powder from good solder paste
2-b Solder powder from dried solder paste

In generally, the main reason of corrosion is thermodynamic instability of metal, that is metal and its alloy is in a high free energy status than other chemical compound (for example, oxide, hydroxide, salt or others), when this situation occurs, metal will transform to lower energy, which is called corrosion.

Metal corrosion is under the basis of the theory of electrochemical, and it’s required four main elements: anode, cathode, electrolyte and constitute current path.

Now let’s parse the mainly metals in solder paste — Sn, Ag, Cu (or other impurities), then under the action of flux medium, numerous galvanic cells with Sn as the cathode and Ag/Cu as the anode are formed, then below chemical reaction will be happened:

Cathode: Sn – 2e → Sn2+

Anode: O2 + H2O + 4e → 4OH

That is: Sn + H2O + ½O2 → Sn(OH)2

Sn(OH)2 decompose: Sn(OH)2 → SnO + H2O

Then chemical reaction of corrosion of solder powder under the moisture in the air can be described as:

The following figure shows the infrared spectrum of succinic acid liquor before and after soaking the solder powder. It can be clearly seen that the soaked liquor contains carboxyl. Therefore, in the solder paste system, except the oxidation reaction of electrochemical corrosion, salinization chemical reaction will be happened too:

Infrared spectrum of Chemical reaction between succinic acid solution and solder powder succinic acid liquor

So now, do you know why solder paste will be dry? And why it is more seriously in hot summer with high temperature and humidity?

Yes, its root cause is not only high temperature in summer, also the humidity is so high (humidity is 70-85% in the summer of Shenzhen City), flux and solder powder will increase the adsorption of water molecules, and due to water is electrolyte of the galvanic cell reaction, it will aggravate the hydrolysis of flux, stimulate the activity of flux, then finally the reaction on the surface of the solder powder is aggravating, and the vicious cycle eventually changes the physical properties of the solder paste.

Then how to solve this problem?

  1. Warm up solder paste before using

Generally, in order to slow down the reaction of flux and solder powder, as well as extend the storage period, the solder paste needed to be stored in a refrigerator with 2-10oC degree. So before using, it is better to take out solder paste and put in standard room temperature for warming up first. A can of 500g solder paste need to be rewarmed at least 2 hours, to make sure its temperature is the same as rooms’. (Normally that period of warming up time is 4 hours in Best Technology.) Otherwise, insufficient warming up will cause the water vapor in the air to condense and enter the solder paste due to the temperature difference, and result in solder paste be dry finally.

  • Environment temperature and humidity

The best storage temp of solder paste is 2-10oC, but the recommended working environment temp is 20-25oC, relative humidity is 30%-60%. (There’re additional humidifiers in the workshop of Best Technology, to make sure suitable humidity in the dry season such as Winter and Spring, and of course the air conditioner in Summer time to decrease the humidity) Usually, the rate of chemical reaction will approximately double, as the temperature increases by 10℃, so the high temperature will increase the volatilization of the solvent in the solder paste and the reaction speed of flux with powder, so the solder paste is easily to be dry. Meanwhile, low temperature will affect the viscosity and expansion of solder paste, and then will cause the poor soldering. At the same time, high humidity will also greatly increase the water vapor entering the solder paste; However, low humidity also affects the volatilization rate of solvent in solder paste.

  • For those solder paste that became dried already, it is better to dilute with flux provided by manufacturer of solder paste.

In a word, when use and store solder paste, we should pay more attention to its temperature & humidity, to make sure high quality of SMT can be achieved. Pls contact Best Technology if you have any questions or comments on solder paste, or SMT.

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X-ray Inspection in PCB Assembly

Wednesday, June 15th, 2022

X-Ray Inspection’s Definition

X-ray inspection is a technology used to inspect the hidden features of the target objects or products. As for PCB inspection, X-ray is commonly used in the inspection of PCB assembly in order to test the quality and find the hidden defects, X-ray inspection is one of the most important steps for quality-oriented PCB manufacturers.

X-Ray Machine

X-Ray Inspection’s Working Principle

Generally, there are three elements in the X-ray devices.

  • X-ray tube—to generate the X-ray photons.
  • Operation platform—to move along with the sample so that the sample can be inspected from different angles and magnification.
  • Detector—it can capture the X-ray through the samples and then transfer it into the image so that we can find out whether there are defects on the printed circuit board.

The Hidden Defects that can be Identified by X-Ray

Since PCB has the higher density with the solder joints hidden and holes buried or blind, X-ray enable us to inspect the quality of the PCB and identify various hidden defects. And there are three common hidden defects that can be inspected by X-ray.

PCB’s Image Under X-Ray
  • Solder bridges—it is a common issue that will occur when the solder joints are so close that they create a connection which is not allowed. And usually, the solder bridges will be covered by some components on the PCB. But they can be easily found with the help of the X-ray device.
  • Solder voids—when gas or flux is entrained during welding, solder voids will be produced, which will lower the thermal conductivity at the solder joint and may cause physical defects. And X-ray can help to  identify the solder voids
  • Pin-hole fills—pin-hole fills issue is a common problem occurring in the plug-in components on the  printed circuit boards. The X-ray device can be used to identify these errors, and can even quantify the missing filling amount.

Our X-Ray Inspection Device

The maximum size of the board that can be put in the device’s operation platform is 510*430 mm, while the maximum inspection size of the device is 435*385 mm. So here is the manifestation of the operation platform’s function. When the size of PCB is over 435*385 mm, the operation platform will move along with the board so that the board can be inspected thoroughly.

And here is a video about operation of our X-ray inspection device.

So, this is the end of this article. In case if you have any questions, you are welcome to contact us via email at  sales@bestpcbs.com. We are fully equipped to handle your PCB  manufacturing requirements.

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What Should be Prepared Before Starting the SMT Process?

Tuesday, February 15th, 2022

SMT, whose full name is Surface Mounted Technology, is the most popular technology in electronic assembly industry. It refers to process on PCB (Printed Circuit Board), putting various electronic components on PCB, such as resistors, capacitors, inductors, and so forth. Also, there are some dos and don’ts in the whole process of PCBA.

As noted previously, there are all sorts of electronic components that will be used in the assembly process of Printed Circuit Board. Therefore, it is extremely important to take some measures to keep a check on static. Here are three steps before entering the SMT workshop.

First, put on anti-static clothes and hats. It is to prevent static existing in clothes and hair from influencing the board, for static has a potential and tremendous destructive power.

Anti-static Clothes and Hats

Second, what we have to do is to put just one hand on static elimination instrument, and do not leave our hand from it until the red light turns to green, which aims to eliminate the static existing in our body.

Static Elimination Instrument

Third, across the air shower door. In this way, dust that is invisible on our body can be blown off in about 5 seconds.

Air Shower Door

Only finishing the three steps above can we enter the PCB assembly workshop. And after entering the workshop, there are also something needed to be prepared.

  • Solder paste. The storage temperature of solder paste is 2-10 degrees Celcius, hence it has a period of regaining temperature, which conducts in the rewarming machine for 4 hours. Then the solder paste should be rabbled in a blender for 5 mins in order to help three ingredients in it to be fully integrated, which can help to achieve a better printing and back-flow soldering effect.
Solder Paste
  • Oven. This machine is used to get rid of the moisture from materials or boards, ensuring that PCB will not be defective due to moisture during the subsequent assembly process. Moreover, different boards have different requirements. But generally, the baking parameter is 105 degrees Celcius, lasting 1.5 hours.
Oven
  • Dryer. It is used to maintain a set temperature and humility of materials and boards that needs to be processed that day, which is also to avoid that moisture does harm to materials and boards after removing the moisture by oven.
Dryer
  • Tension test of stencils. Before manufacturing, the stencils’ uniformity should be tested by tensiometer, which mainly tests the four corners and the center part of the stencil, guaranteeing the solder paste printing quality. And the parameter should be between 30 and 45.
Stencils

To sum up, although there are lots of preparations should be done before starting the formal assembly process, each of them is significant, for they will probably influence the quality of boards directly. Besides, only a good preparation can make a certain that the follow-up process can keep going. Thus, it is a must to prepare well in advance.

And Best Technology is an experienced electronic company. It not only can provide PCBA service, but can provide other services, such as FPC, FR4 PCB, Rigid-flex PCB and so on. And if you have any questions about SMT, or any other questions about assembly, you are welcome to contact us.

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