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Archive for the ‘PCBA’ Category

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.

The Advantages of Surface Mount Technology of a printed circuit board

Friday, March 19th, 2021

Surface-Mount TechnologyÂ has been the industry standard for assembling printed circuit board. It has maintained its popular due its wide array of advantages and relatively few drawbacks. For more than 15 yearsâ€™ experience,Â Best TechnologyÂ has been offering surface-mount service for worldwide customers, and SMT service become a great part of our business.

See some photo which we are do assembly for our customer this month.

Top Advantages of Surface-Mount Technology

Smaller size and reduced weight are the two main advantages to SMT. Components can be aligned closer together and end products will be more compact and light weight.

Here are additional benefits of SMT:

1.Component placement auto correctly â€“ there is no alignment between the PCB solder pads and components pads to avoid placement errors.

2.Low cost:

The advantage of small size up to 0201. One set, SMT typically requires lower production costs than through-hole placement. The size of the board is reduced, the number of drilled holes is reduced, and routing of traces is reduced. So bring down the cost of the whole project.

3.Design flexibility â€“ You can combine through-hole technology and SMT manufacturing on the same board for greater functionality.

4. Printed circuit boards created with the SMT process are more compact, providing higher circuit speeds. (This is the main reasons most manufacturers choose for this method.)

5.Higher circuit speeds â€“ Most manufacturers rate this the number-one benefit.

Lower resistance/induction â€“ High-frequency performance reduces unwanted consequences of RF signals.

6. Quick Turn Around

Using Surface-Mount Technology, it can save lots of time, SMT is a much more streamlined manufacturing process compared to through-hole. Time is saved because components are applied using a solder paste instead of drilling holes in the PCB

7. Quantity â€“ More components can be positioned using both sides of the circuit board, creating more connections for each component. Fewer circuit boards are needed for devices.

8. Stability â€“ Better performance delivery is realized with vibration mechanical conditions. SMT connections are more reliable, it can reduce the dis connection risks during the final test.

Best TechnologyÂ offers expertÂ surface-mount technologyÂ services in China, along with manufacturing bare printed circuit board, flexible circuits,Â and MCPCBÂ fabrication. With more than 15 years rigid PCB board experience, Best Technology has the resources, equipment, and know-how to produce your PCBs quickly and reliably.

Call Best Technology nowÂ and let us become your partner of PCB assembly service.

How to clean the PCB assembled boards after soldering?

Friday, June 19th, 2020

Best Technology is a full turn-key assembly service company, we can supply the assembled board with very nice and clean surface.

Do you want to know how we control the cleaning process of PCBA? We would like to share the full cleaning process.

As we know, flux is used when soldering electrical components to a printed circuit board.

After assembly process finished, we need to remove all the unnecessary flux paste or other solder flux/ residue in order to avoid any quality issue.

Although it is a simple work, but to prepare some tools and preparation is necessary and important. Like wash board water, dust-free cloth, brush,Tweezers, static bracelets, finger gloves

Here is the how the cleaning process we made:

Step1:

Use brush to brush the solder joint and solder flux on the soldered PCB. Applying some alcohol or acetone onto the brush, do not use too much pressure, as this may cause the solder point to break. Repeat the procedure as necessary, to remove remaining flux residue on the PCBA.

PCB assembly — Step1: Brush the solder joint and solder flux on the soldered PCB

Step2:

Wipe with a clean dust-free cloth to clean the assembled PCB.

Keep board clean and tidy to make sure no impurities and finger marks. Do the same process for bottom side.

Step3:

When above step finished, keep the board for an extra day to let the board dry enough before packing. Best QC guys will do final inspection for the finger prints under light. this will be helpful to check the cleaning result further.

Step4:

Finally, use dust-free cloth to do the final cleaning and let the board dry and clean enough before package.

PCBA Cleaning process — Step4: use dust-free cloth to do the final cleaning.

Above are the process for how we clean the assembled boards.

Best Tech is a very professional manufacturer in printed circuit board and assembly. We clean each of assembled boards as the procedure we showed above.

If you are interesting to know more process for how we control the quality for the PCB assembled boards, contact us at any time, we will show you more.

PCB & MCPCB – Best Technology

Archive for the ‘PCBA’ Category

Why Solder Paste became Dry and How to Solve This Problem

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X-ray Inspection in PCB Assembly

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Electrostatic’ s Power-Trivia Series 2

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What Should be Prepared Before Starting the SMT Process?

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Via Tented, Via Filled & Via Plugged

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The SMT production progressing

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Notes for cleaning PCBA

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What’s fiducial marks on the PCB?

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The Advantages of Surface Mount Technology of a printed circuit board

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How to clean the PCB assembled boards after soldering?

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