Archive for the ‘FAQ’ Category

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.

  1. 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.
Copper Core PCB
  • 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.
FR4 PCB
  • When cleaning the PCBA board, protect the components and labels on the board. Otherwise, the mounted and welded PCBA board will be wasted.
Aluminum Core PCB

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 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.

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Aluminum vs Copper Core PCB

Wednesday, May 19th, 2021

In Best Technology, currently the most common metal used for Metal Core PCB manufacturer are Aluminum, Copper. Today let’s talk about the main differences between aluminum substrate and copper substrate, hoping to help you choose the right substrate in future design projects.

Although they both share similar properties and functions, there are still a few variations between the two kinds of metals. Some of the key differences between aluminium and copper core PCBs are explained in the points below.

1. Thermal Conductivity

The thermal conductivity of copper substrate is up to about 400(W/mK) and the thermal conductivity of aluminum substrate is generally about 200W(W/mK). The thermal conductivity is higher, the transfer efficiency will be better, and the heat dissipation will be better, then the working life will be longer.

 Thermal Conductivity

2. Electrical Conductivity

Both aluminum and copper, being metals, are electrical conductors of electricity, although the exact degree of this varies between the two metals. When it comes to electrical conductivity, copper has a clear advantage over aluminum. In other words, in applications where there is a need for efficient electrical conductivity, copper makes for an ideal pick.

 Electrical Conductivity

3. Electrical Resistance

Resistance is very important when it comes to PCB design, as it can have an effect on the overall function and stability of the component. Given that copper has a higher density than aluminum, it tends to have a lower resistance than aluminum, so copper is an better choice where there’s a requirement for thinner circuits and faster electricity transfer.

Electrical Resistance

4. Weight

Since copper has the higher density for per unit area, the weight of copper PCB is much heavier than aluminum PCB for the same design.

In applications where light-weight construction is required more than anything else, aluminum is the preferred material of choice. On the other hand, applications where weight is not much of an issue, tends to be the ones where copper is widely used.

Weight

5. Application

Copper core PCB is the best heat dissipation among all MCPCB, so it’s mostly used in automobile headlights, taillights and some high-tech electronic products (unmanned aircraft, mining machine) high-power lighting equipment. The aluminum core PCB is mostly used in indoor lighting, energy saving lighting, street lighting and other energy-saving lighting electronic products.

Application
Application

In conclusion, due to the above different parameters and performance, the cost of copper is generally more expensive than aluminum. If you have other questions about MCPCB, welcome to contact us .

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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 what’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 holes types
Fiducial holes

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:

PCB panel drawing Best Technology
Fiducial holes on a panel

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.  

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Main types surface finish of FR4 Printed wiring board

Wednesday, November 4th, 2020

Printed Circuit Board surface finish is a coating between bare FR4 board and components. The main function for surface finish is to protect the exposed copper circuitry and provide a solderable surface when assemblingsoldering) the components to a copper clad PCB board.

Most of the Rigid Circuit board company can make several different types of surface finish. Best Technology as a leading custom FR4 printed circuit board manufacturer since year 2006, it could provide following different finish.
HASL
Lead-free HASL
Immersion Tin/Immersion Silver
OSP (organic Solderability Preservative)
Gold
ENIG (Electroless Nickel Immersion)
Hard Gold
Wire bonding Gold

As the surface mounts assembly service became more complex and needs to conform to new regulations like RoHS and WEEE. People maybe face the question how to choose a suitable surface finish for your FR4 Copper board?

Before decide to choose suitable surface of copper conductors circuit board, you may need to take the cost, RoHS, your components type, PCB assembly method, factory circuit fabrication capability, and rigid board circuit testability into consideration.
Basis on above information of copper foil PCB, we would like to make a explain PCB finish in detail, wish this may help when you make decision at circuit board design and manufacturing.

HASL/Lead Free HASL
It is a most popular surface finish, and the cost is low and easy to repairable, it is acceptable for simple SMT. But the surface is uneven, it is not suitable for fine pitch components and not good for plated through-hole(PTH). In other way, it is poor wetting.
Material different with same finish
HASL(standard):Typically Tin-Lead
HASL(Lead Free):Typically Tin-copper, Tin-Nickel, without lead
The thickness will conform to IPC 6012 class 2 standard

Advantages of HASL-LF
Excellent solderability
Inexpensive / Low cost
Widely Available and used
Easy reworkable
Allows large processing window
Long industry experience / well known finish

Disadvantages of HASL-LF
Uneven surfaces for printed circuit board
No good for fine pitch components from Samtec/Hirose/Molex
Thermal shock
Solder Bride for circuit board assembly
Plugged or reduced PTH’s
Not suited for < 20mil pitch SMD & BGA
Bridging on fine pitch
Not ideal for HDI products

Immersion Tin

Advantages
Flat surface
No Pb
Good for fine pitch / BGA / smaller components
Mid range cost for lead free finish
Press fit suitable finish
Good solderability after multiple thermal excursions
Easy reworkable

Disadvantages
Very sensitive to handling – gloves must be used
Tin whisker concerns
Aggressive to solder mask – solder mask dam shall be ≄ 5 mil
Not recommended to use peelable masks
Exposed tin on final assembly can corrode
Not good for multiple reflow/assembly process
Difficult to measure thickness

OSP (organic Solderability Preservative)
OSP(organic Solderability Preservative) same with HASL, lower cost but the OSP have flat surface, and it is not good for PTH components, sensitive and short shelf life, it is very easy come to oxidation.

Advantages
Flat surface
No Pb
Good for fine pitch / BGA / smaller components
Inexpensive / Low cost
Easy reworkable
Simple Process
Disadvantages
Not easy to measure thickness
Not good for circuit copper board plated through-hole(PTH)
Short Shelf Life
Maybe cause ICT issue
Exposed Cu on Final assembly
Handling sensitive– gloves must be used and scratches avoided

The above surface finish of Printed Wiring Board compared with Gold finish, the cost is corresponding cheaper, but in my coming blog, I would like mainly to explain Gold finish for printed circuit board fabricator with 13 years rich-experienced in FR4 PCB custom contract manufacturer.

If you have any question about the printed circuit boards (PCBs). Warmly welcome to send mail or call Best Tech.

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Why don’t use BeO as substrate to make DBC ceramic PCB?

Wednesday, September 9th, 2020

It is widely known that BeO with high thermal conductivity (200-250W/m.k).

High dielectric constant 6-7 (0.1MHz) and dielectric loss tangent is 10-4 (0.1GHz).

It is ideal material for ceramic PCB, lots of engineers want to use it as DBC ceramic PCB substrate.

But it is unfeasible, the powder of BeO is extremely poisonous.

The poison gas is produced by the reaction between oxygen, Cu and BeO under

1065-1085 degrees Celsius, so it is limited to make cooper on BeO substrate,

it has caused AlN (Aluminium Nitride) is becoming more and more popular.

Though BeO is unfeasible for DBC technology, but it is feasible for thick film technology.

Because when doing the conductor (Au or AgPd) on BeO substrate, we use silk-screen printing, no need to under high temperature environment, there is no chemical reactions.

Below the manufacturing process for your reference.

Here is the photo of BeO with AgPd conductor.

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What’s the advantages for AMB ceramic PCB comparing with DPC, DCB, LTCC, HTCC, thick film ceramic PCB?

Tuesday, August 18th, 2020

As we know, there are all kinds of ceramic PCB, DPC ceramic PCB, DBC ceramic PCB, LTCC ceramic PCB, HTCC ceramic PCB, thick film/thin film ceramic PCB.

Very few people know that there is AMB (Active Metal Bonding) ceramic PCB.

Do you know what’s the advantage for AMB ceramic PCB compare with other ceramic PCB (Al2O3/AlN/BeO/Si3N4 PCB)?

For AMB PCB, the substrate can be AlN ( Aluminium Nitride) and Si3N4 (Silicon Nitride) normally, AlN is the most popular. It is widely known that AlN with very high thermal conductivity ( Theoretical Value is 320W/m.k).

Using AMB technology to combine the oxygen-free copper and AlN material under high temperature, AlN with smaller thermal resistance, lower coefficient of thermal expansion and more stable partial discharge capability.

Compared with the traditional DBC or other substrate, the Aluminum Nitride copper-clad ceramic substrate made by the AMB technology with higher bonding strength of the copper layer and better cold and hot cycling characteristics.

So it  is widely used in the field of IGBT, especially for the high-power device control module.

AMB with competitive price and the copper thickness can be much thicker.

AlN max 300um
Si3N4 max 1200um

For more details, please contact me sales@bestpcbs.com 
I will update the manufacture process at the end of this month.

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How to avoid circuits issue while the production process ?

Monday, July 13th, 2020

As we all know, the short & open circuits is a very common issues for the Printed Circuits Board, especially for the extra thin PCB, because its substrates thickness are very thin, generally from 0.4mm-0.15mm, so the circuits will be easy to be broken if we didn’t control the production process well.

So, you may want to know, as an experienced PCB manufacturer, what we will do to avoid the circuits issues?

Here let me show you what we do:

Firstly, after the process of copper plating, we will put the boards into our washing line to remove those drilling burr, surface oxide layer, etc.  To make sure the boards are fully clean before start the traces making process.

pcb washing
pcb washing

Actually, most of the open and short circuits problem are caused by the film scratching, so each operation while the pattern transfer process is very important.

That’s also why the exposure and developing need to be processed in the dust-free workshop. We will use the rack to place each PCB board separately, to avoid the touching between PCB.

pcb explosure and developing
pcb explosure and developing

After the circuits etching out, we will take the boards to do the AOI testing, to check if there are any broken circuits, short gaps, protrusions, copper surface garbage and other problems. If there is, our machine will alert the problem, and we will fix the problem or scrap the defectives boards, with this process to prevent the defective boards move to the next step.

Most importantly is that we will do the first article inspection for all the boards, as long as we found the circuits issues while the AOI process, we will not take the whole batch boards go ahead.

aoi testing
aoi testing

Besides, the operation standard while the etching process is also very important for how the traces being. So, our production team will control the running speed of the etching machine very strictly. If it is a PCB with o.5oz bottom copper , only allow walk 1.4 meters at per minute, if 2oz, walk 0.8m one minute.

etching pcb
etching pcb

Except above process, all the boards will be required to do a final electrical testing before move to the packing. For prototypes, we will use flying probe testing. For volume, we will open the E-testing fixture to do the testing.

In our company, for the extra thin PCB, if the boards thickness lower than 0.2mm to do the flying probe testing, it needs to be tested before the outline process, because the boards are too thin to support the boards well while the flying probe, it will fall down easily.

flying probe testing and electric testing
flying probe testing and electric testing

Of course, our QC people will do the double visual inspection to make sure all the boards are being well made.

fr4 pcb inspection
fr4 pcb inspection

We always try our best effort to prevent any defective boards send to customers.  

Quality and Customers Scarification, it is always our company’s pursuit.

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How to improve the gap between the convexity and LED pad?

Saturday, July 11th, 2020

About the SinkPad copper core PCB, all is known that convexity is very important, the height of convexity is about 0.2mm-0.25mm.

We need to know what’s the reasons caused the gap between the convexity and LED pad is big.

  1. We make the copper core with convexity firstly, then make the circuit/panel board (FR4PCB/BT PCB) and finally do the lamination for cooper core and circuit board.
  2. The tolerance for convexity is +/-0.05mm-0.075mm.
  3. The tolerance for circuit/panel board is +/-0.13mm.

If we do negative tolerance for convexity and positive tolerance for circuit/panel board, then it will cause the gap very big.

See below picture and details.

For example, the size of convexity is 0.5mm, after negative tolerance -0.075mm, it will be 0.425mm and each side will be 0.0375mm smaller.

For the circuit/panel board, the gap between convexity is 0.2mm, after positive tolerance +0.13mm, it will be 0.33mm and each side will be 0.065mm bigger.

So finally, the gap will be 0.2mm+0.0375+0.065mm=0.3025mm. It is about 50% bigger than original size.

sinkpad pcb
sinkpad pcb
sinkpad pcb
Big gap between convexity and LED pad

How to improve that problem?

  1. Making the copper core with convexity according to design.
  2. Measuring the dimension of convexity before making the circuit/panel board, then making the circuit/panel board according to the convexity dimension with compensation design.
  3. Do Positive tolerance for convexity and negative tolerance for circuit/panel board, the gap will be much more smaller.

For example, the size of convexity is 0.5mm, after negative tolerance +0.075mm, it will be 0.575mm and each side will be 0.0375mm bigger

For the circuit/panel board, the gap between convexity is 0.2mm, after positive tolerance -0.13mm, it will be 0.07mm and each side will be 0.065mm smaller.

So finally, the gap will be 0.2mm-0.0375-0.065mm=0.0975mm. It is about 50% smaller than original size.

dtp pcb
dtp pcb
DTP PCB
Good gap between convexity and LED pad

For more information about SinkPad PCB, please click

https://www.bestpcbs.com/products/multi-layer-sinkpad-board.htm

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In order to reduce the cost, can SinkPad PCB use aluminum base instead copper base for heat dissipation?

Wednesday, June 24th, 2020

SinkPad PCB is a type of Copper base PCB used in thermoelectric separation application. It generally used for high power LED, the pad of LED touch the copper base directly, so that the heat generated by LED will dissipate quickly, which can achieve the best heat dissipation and conduction.

sinkpad gerber
sinkpad gerber
sinkpad pcb
sinkpad pcb

In another words, it is a technology that require to increase the path of the LED pad to the copper base to accelerate the heat emission from the base material. The copper base is vital while it also cost higher.

Then in order to lower cost, can SinkPad PCB use aluminum base instead copper base for heat dissipation?

The answer is NO. As you can see the below manufacturing steps, the SinkPad will etch the copper base into convex platform with Copper Etching Solution, then hollow out the Double Layer FR4 PCB, and do lamination with the convex platform.

sinkpad pcb manufacturing steps
sinkpad pcb manufacturing steps

However, regarding of current technical conditions, since aluminum or aluminum alloy cannot directly react with acid, the reaction process is too complex and difficult to control, which will increase the difficulty of etching the LED pad platform. Considering the scrap rate, the process of etching LED pad platform with aluminum is more complex and the overall cost is higher.

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Why don’t use BeO as substrate to make DBC ceramic PCB?

Monday, June 22nd, 2020

It is widely known that BeO with high thermal conductivity (200-250W/m.k). High dielectric constant 6-7 (0.1MHz) and dielectric loss tangent is 10-4 (0.1GHz), extremely high working temprature. It is ideal material for ceramic PCB, lots of engineers want to use it as DBC ceramic PCB substrate.

But it is not popular in ceramic PCB market, comparing with Al2O3, AIN, Si3N4, or ZrO2, as the powder of BeO is extremely poisonous.

The poison gas is produced by the reaction between oxygen, Cu and BeO under 1065-1085 degrees Celsius, so it is limited to make cooper on BeO substrate, it has caused ALN (Aluminium Nitride) is becoming more and more popular.

Right now, only few countries are using BeO to make ceramic PCB, such as USA, Russia and China. USA had biggest capability to make BeO , and here in China, there’re still some companies to make BeO raw material and among them, a few companies to produce direct copper bonded (DCB) on BeO because of environment limitation.

Though BeO is not popular for DBC technology, but it is feasible for thick film technology, because when the mentalization of Ceramic PCB, the conductor (Au or AgPd) on BeO substrate was made by silk-screen printing, and drying temperature is only around 850C, no need to under high temperature environment, so there is no chemical reactions, no environment issue.

Below the thick film ceramic PCB manufacturing process for your reference.

https://www.bestpcbs.com/products/thick-film-ceramic-pcb-manufacturing-process.htm

Here is the photo of BeO with AgPd conductor.

BeO with AgPd conductor
BeO with AgPd conductor

Welcome to contact us if you have better idea, or different comments on BeO ceramic PCB, communation will make us becoming better and better.

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