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Archive for the ‘PCBA’ Category

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 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.

Part 3: The Difference Between Solder Mask and Solder Paste

Solder mask is a formal part of PCB, but solder paste ONLY for PCB assembly.
Solder mask is not allowed on the solder pads while solder paste can be printed on the solder pads openings.
Solder mask is used for applying solder mask ink, but solder paste is used for applying paste.
Solder mask has many available colors, but paste mask visually gray.
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.

How To Do Failure Analysis In Printed Circuit Board

Saturday, October 29th, 2022

Nowadays, printed circuit board plays a more and more important role in electronic products, whether for personal use or commercial use, failure PCB can effect the usage of electronic products and cause a serious consequence. So, how to quickly detect the PCB fault problem?

Here, Best Tech summarized seven methods to locate fault PCB quickly.

Use testing equipment

The typical equipment including Automated Optical Inspection (AOI) equipment, X-Ray Fluoroscopy, Optical Microscopy, 1000x magnifying glass. When some failures happen and we don’t know what is the specific position, properly use of these detection devices can help us quickly locate the faulty PCB.

Visual inspection

Visual inspection is the most common and easy method to position those defectives in printed circuit board. It can identify defects such as overlapped marks, solder joint short, signs of overheating circuit boards, and burned components. When some problems are difficult to identify with our naked eye, magnifying glasses can help to identify some short circuits, welding bridges, open circuits, solder joints and circuit board wiring cracks, component offset, etc.

Components inspection

If the printed circuit board was assembled with some electronic components, we can perform a components inspection to locate the failure. Especially when low resistance is detected between the component pins, it is best to remove the component from the PCB circuit for specialized testing. If the resistance is still low, then this component is the culprit, otherwise further investigation will be required.

Power on printed circuit board

Visual inspection is only suitable for checking the appearance of outer layers of the circuit board, instead of for checking the inner layer of the circuit board. If there are no visible defects in the appearance, you can power up/on the board and perform a more detailed test to determine whether the board is working properly or not.

Low voltage measurement

The first thing to confirm is whether the voltage of each chip power pin is normal, and then check whether the various reference voltages are normal, and whether the working voltage of each point is normal. Since the copper trace on the circuit board has resistance, the voltage generated through different parts of the copper trace is also different. Then you can use a voltmeter or multimeter to measure the voltage between different parts along a short. If you find that the voltage value is getting smaller and smaller, you are getting closer to find out a short circuit.

For a simple example, when a typical silicon triode is on, the BE junction voltage is around 0.7V, while the CE junction voltage is around 0.3V or less. If the BE junction voltage of a triode is greater than 0.7V (except for special triode, such as the Darlington tube), the BE junction may be open.

Touch circuit board with your finger

In general, when some failure happened, some areas on the circuit board will be getting more and more heat. In this time, we can try to touch the circuit board with fingers to find out areas with heat, and it will help us to pinpoint the problem. However, be careful to use short-circuit copper trace power supply and avoid burns or electric shock.

Repair short/open

After identifying a short or open circuit on the PCB, the next step is to isolate the problem. While this is easy to do on the outer surface of the board, it is a challenge for the inner layers. Possible solutions include drilling through holes or cutting appropriate external copper traces.

This is the end of this article, if you have more better methods to locate the failure printed circuit board, warm welcome to contact us, we can analyze together.

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?

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)₂decompose: 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?

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 2-10^oC 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 2-10^oC, but the recommended working environment temp is 20-25^oC, 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.

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 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.

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.

Electrostatic’ s Power-Trivia Series 2

Monday, April 18th, 2022

Last time we have known that electrostatic discharge (ESD) account for the highest proportion of causes leading to the failure of high electrostatic sensitive devices and the generation of it. Therefore, today we are going to talk about what kind of damage the static will cause to the Printed Circuit Board and how to avoid it.

The Influence of Electrostatic

Under different circumstances, the electrostatic voltage carried by the human body ranges from hundreds of volts to thousands of volts. And when people touch the electronic components, there will be ESD, resulting in the damage to devices and the reduction of reliability. To make matters worse, ESD will break down the device and directly scrap the product.

Besides, the ESD will lead to a large pulse current, which will generate a lot of heat in the chip and printed circuit board, making them burn out. Moreover, the integrated circuits (IC) are built with denser lithography lines than before so that their ability to withstand electrostatic discharge becomes weaker. Therefore, it is necessary to prevent it.

Elimination of Electrostatic

Since the static will has a great impact on the PCB and electronic components, it is extremely significant to take precautions against the electrostatic by taking some measures. And here are some measures carried for eliminating the electrostatic in our workshop.

Putting on anti-static clothes and hats. It is to prevent static existing in clothes and hair from influencing the board.

Wearing anti-static wrist straps. The principle is to discharge the static from the human body to the ground through the wrist strap and grounding wire.

Using static elimination instrument. 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.

Keeping a certain humidity in the workshop. Higher humidity is not prone to ESD. The higher the humidity is, the easier it is to conduct electricity. As a result, electrostatic cannot be stored in our body.
Using anti-static packaging. When packaging, we have different packaging ways, such as anti-static bags, anti-static bubble film and so forth. And what to be used in packaging is up to our clients.

To sum up, electrostatic will cause damage to the Printed Circuit Board and electronic components so that it is necessary to take some measures to prevent it.

And this is the end of this trivia. If you would like to know more about PCB, you are welcome to contact us.

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.

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.

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

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.

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.

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.

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.

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 PCB A 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.

Via Tented, Via Filled & Via Plugged

Monday, December 20th, 2021

Via Tented, Via Filled (filled with solder mask) & Via Plugged (Via In Pad â€“ Conductive material or Non-Conductive material)

One of the most confused idea during our PCB design is the difference between Via Tenting, Via Filling and Via Plugging. Designers often get mixed up between them and fail to take full advantage of the process.

Today, let us discuss them, so that you can be confident in specifying your design requirements clearly when submitting PCB files to Best Technology before final manufacturing.

Via Tented

What is via?

A plated through hole (PTH) in a Printed Circuit Board that is used to provide electrical connection between a trace on one layer of the Printed Circuit Board to a trace on another layer. Since it is not used to mount component leads, it is generally a small hole and pad diameter.

A. Three methods and definitions of via processing

There are three methods for via processing: via hole opening & via hole cover oil & via hole plug oil

1. Through hole opening window: it is the tin on the solder ring of the via (the tin is exposed like a plug-in pad). The window is usually used to debug the measurement signal. The disadvantage is that it is easy to cause a short circuit.

2. Through hole cover oil: it is the welding ring of the through hole (via) covered with solder mask ink

3. Through hole plugging oil: refers to plugging the hole with ink.

Secondly, the inspection standards for a processing method

1. Through-hole opening window is like a plug-in pad, and the window is sprayed with tin. Inspection standard: tin can be tinned, and tin can be easily tinned.

2. The inspection standard of the via hole cover oil: it is not easy to tin in the patch.

3. Inspection criteria for via plug oil: First, it must be opaque, and it must be covered and blocked by ink.

Finally, we are talk for comparison and distinction between via hole cover oil and via hole plug oil:

1. Via plug oil This process is an important supplement to via plug oil, so generally high-quality boards will require via plug oil. And often many engineers who are just entering the industry are stupid and unclear. So how do you distinguish between the two?

2. The requirement of via hole cover oil is that the ring of the via hole must be covered with ink. The emphasis is to ensure the thickness and coverage of the ink on the edge of the hole. The key control is that the ring does not accept false copper exposure and orifice oil. Thin

3. Through hole plugging oil is the production of plug holes with ink inside the holes of the through holes. The emphasis is on the quality and density of the plug holes. After the holes are plugged, no light can be transmitted.

4. The method of plugging the via hole is to first fill the via hole with ink to block the via hole, so that the ink on the solder mask will not flow into the via hole, so as to achieve the situation that the via hole does not appear yellow. (If you have strict requirements and place an order for via hole cover oil, the cover oil is usually not full or yellowish, you can change it to via hole plug oil later). In addition, the smaller the vias are, the easier it is to plug them. The vias of the fortress oil are not easy to be too large (the circuit board proofing plugging oil is directly plugged with ink, and the printing tape is plugged. It is recommended that the vias that need to be plugged are designed to be <0.5mm. This is also free; no additional money is required).

If you have more question Via Tented, Via Filled& Via Plugged, warmly welcomed to contact Best Tech for more FR4 design service.

The SMT production progressing

Thursday, November 18th, 2021

SMT (Surface Mounted Technology) is the most popular Technology and process in electronic assembly industry. SMT refers to a series of process processes based on PCB. Due to the better outcome and higher efficiency, SMT has become the primary approach used in the process of PCB assembly. In some extent, the turn-key service is a way to reduce the cost.

There are the SMT progressing in the following.

1. Solder paste printing: The function is to print the solder paste to the PCB pad to prepare for the welding of components. The screen-printing machine is located at the front end of SMT production line.

2. Part mounting: The function is to accurately install surface assembly components into fixed positions on the PCB. The equipment is the SMT machine, located behind the screen-printing machine in the SMT production line.

3. Furnace curing: its function is to melt the patch adhesive, so that the surface assembly components and PCB board firmly stick together. The equipment used is the curing furnace, located behind the SMT machine in the SMT line.

4. Reflow welding: The function is to melt the solder paste, so that the surface assembly components and PCB board firmly stick together. The reflow furnace is located behind the SMT machine in the SMT line.

5. AOI optical detection: its function is to detect the welding quality and assembly quality of assembled PCB board. The equipment used is automatic optical detection (AOI)

6. Maintenance: its function is to detect the failure of the PCB board for repair. The tools used are soldering iron, repair workstation and so on. Configured after AOI optical detection.

7.Dividing board: its function is to cut PCBA of multiple connecting boards, so that they are separated to form a single individual, generally using V-cut and machine cutting.

8. Grinding plate: its role is to scrub the burr parts to make them smooth and flat.

9. Washing plate: its function is to remove welding residues such as flux and other harmful to human body on assembled PCB board and manually clean it.

Turnkey service reduces customers’ time in contacting with multiple suppliers for separate steps in PCB assembly manufacturing. And the scientific order arrangement system allows customers to get PCB assembly products with higher quality and less cost in a shorter time than the traditional way of PCB assembly.

Notes for cleaning PCBA

Monday, October 18th, 2021

PCBA includes components assembly and DIP plug-in, in the whole process, there will be reflow soldering, wave soldering, manual soldering, due to the current Electronic products are getting smaller and smaller, and the size requirements of PCBA are getting smaller and smaller, but the requirements for quality (including product reliability and stability, etc.) are getting higher and higher. Many customers require PCBA boards with conformal coating to increase stability and reliability and ensure product quality and performance. But the PCBA board must be cleaned before with conformal coating.

Because there will be a variety of flux residues on the soldered MCPCB board, some of which are acidic, soluble and corrosive, etc., if these residues are not cleaned, the coating will also cause very great damage to the product. In this blog I’d like to share some notes for cleaning PCBA.

PCBA board after soldering, should be cleaned as soon as possible (flux residue will produce corrosion over time), cleaning residual flux and other pollutants on PCBA board.

When cleaning the PCBA board, prevent the cleaning agent from intruding into the unsealed components to avoid damage to the components. After cleaning, it should be placed in the oven at about 30-50 degrees, baked for about half an hour, and then removed after drying PCBA board.

When cleaning the PCBA board, protect the components and labels on the board. Otherwise, the mounted and welded PCBA board will be wasted.

Cleaning PCBA board affects the life and reliability of electronic products. Some of PCBA boards are not cleaned, which may lead to short circuit and leakage, leading to unqualified products and many failures, increasing the cost of recovery and maintenance, so it is not worth the loss to clean PCBA boards.

Best Technology has our own SMT factory and can help our customers to buy the components at the same time. If you have any new inquiry of PCBA, welcome to send it to me then I can send you the quotation for comparison with your other suppliers.

What’s fiducial marks on the PCB?

Saturday, April 24th, 2021

You may ever be recommended by some PCB manufacturers to add the fiducial holes on the board edge. Do you know what is fiducial marks and whatâ€™s the purpose for this kind of holes in a PCB?

Now, let me to show you something for what is the fiducial holes.

Fiducial holes, we also call it fiducials mark, while we assemble a PCB, it will need to locate the positions for each component, and it is positioned based on the fiducial mark as the reference point.

There are 3 types fiducial marks, first type is fiducial marks on a single board, second type is the fiducial marks on a PCB panel, third one is the fiducial marks for some single component on the board.

Here are the pictures for you to understand the types of the fiducials.

Fiducial mark on a single board is designed for positioned all circuits features on a single board. It is necessary to have a fiducial mark on a single board.

And fiducial marks on a PCB panel is used to assist positioning the circuits.

For the fiducial mark of a single component, it is designed to position the fiducial mark of a single component, which can improve the placement progress (For QFP, CSP, BGA and other important components must have the fiducial marks).

So, it is important to add the fiducial holes on a PCB board.

Also, while we make the panel for the PCB board, on the diagonal of the four corners, it is required to have 2 fiducial points at least on 2 diagonal corners. you can also place 4 marks on the four corners, but generally, assembly plant will only need 2 marks for recognize.

See below a PCB panel for reference:

In the other hand, while you design the PCB, please try not to put the silk screens, pads, traces etc. within 2mm of the optical fiducial marks. Otherwise, the SMT machine will not be able to recognize the optical fiducial on the PCB boards.

And if you add the fiducial holes on the area which without any circuits, to avoid the holes being etching while the process, so generally we suggest to add a metal circles around the fiducial holes, to make it more obviously on the boards.

If you have any new PCB design which you also want to add the fiducial marks.

You are welcome to contact Best Technology for a help and we will show our best help for you.