Archive for January, 2023

Why HASL Surface Treatment Is Not Suitable For Sink Pad MCPCB?

Thursday, January 12th, 2023

Sink Pad MCPCB is a special type of metal core PCB (short for MCPCB), the working principle is through the sink heat pad solder direct to the metal substrate (commonly copper or alumina substrate), so people also call it as Thermal pad MCPCB. Sink Pad MCPCB is popular recently due to its excellent heat dissipation and thermal conductivity. Since the copper is easy to get oxidation, coating a metal film is good for protecting the surface, such as ENIG, ENEPIG or OSP. Lead-free hot air solder leveling (HASL) also is a kind of surface treatment, but why we don’t suggest to apply it? Let me explain with you.

Why is HASL not recommended?

  • Substrate

From the substrate aspect, due to the HASL process is to first dip the solder on the circuit board, then dip the solder flux in the melting, and finally blow off the excess solder on the printed board with the hot compressed air in the air knife through the two air knives, at the same time to eliminate the excess solder in the metal hole, so as to get a bright, smooth and uniform solder coating. Since most of customers prefer choose copper substrate as the base material (Aluminum core sink pad PCB thermal conductivity only could be 235 W/m.k, while Copper core sink pad PCB thermal conductivity could reach to 400 W/m.k). However, copper base is much heavier than alumina core, during the hot air knife scraping tin process, the copper surface is easy to be scratched and get damaged to affect the poor appearance and a short circuit risk. This is one of the reasons why HASL is not suitable for Sink Pad PCB.

  • Structure

From the structure of the Sink Pad MCPCB, the LEDs Chip Thermal Pads solder contact to the copper substrate directly, no dielectric between LEDs heat out pads and the Metal core. As you can see the stack up as below, what Sink PAD PCB laminate is pure film, the adhesion is not very good, so there’s a risk of delamination if do HASL (lead free).

  • Chemical

From the chemical aspect, due to the HASL (lead free) has the process of return the film, the potion will react with the copper chemically, which will bring the poor coating and poor adhesion, so we don’t recommend to use HASL on the Sink Pad MCPCB.

Advances of the Sink Pad MCPCB

  • Thermal conductivity 235 To 400 W/m.
  • Super good heat dissipation
  • Power LED junction temperature
  • Longer LED life
  • Most economical direct thermal path solution
  • Direct thermal path
  • Different structure can be made according different design needs

When can we use Sink Pad MCPCB?

With so many kinds of PCB types, when and where can we use the Sink Pad MCPCB?

  1. The copper metal core has high density, strong thermal conductivity and carries heat effectively. That means, it is possible to dissipate the same heat using a smaller sink-pad MCPCB, as compared to regular MCPCBs. So it is suitable be used in small applications which need to apply in high temperature.
  2. Very popular with high power LED mounting, sink-pad MCPCBs with their thermoelectric separation structure, can minimize the lumens depreciation of the LED, thereby prolonging the life of the LED lamp. Sink-pad MCPCBs are suitable for mounting high-power LED lamps and COB packaged LEDs. Moreover, manufacturers can tailor the sink-pad MCPCB to match the different design requirement needs of any LED.

Best Technology is a professional Sink Pad MCPCB manufacturer for more than 16 years in Asia, we have strong engineering team and specialized sales team can provide most suitable solutions for your applications in a very short time. What we can provide not only include single layer Sink Pad MCPCB, we also can produce 2 layers, double layer and multi-layer Sink Pad MCPCB. View https://www.bestpcbs.com/products/sinkpad-board.htm to know our capability about Sink Pad MCPCB.

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Everything you should know about Tg in PCB

Wednesday, January 4th, 2023

Working temperature changes can have a significant influence on the operation, reliability, lifetime and quality of products. Temperature rises results in materials expanding, however, the substrate materials that PCB are made of have different thermal expansion coefficients, this causes mechanical stress that can create micro-cracks that may be undetected during electrical tests carried out at the end of production.

Due to the policy of RoHS issued in 2002 required lead-free alloys for soldering. However, removing lead directly results in the rise of melting temperature, printed circuit boards are therefore subject to higher temperatures during soldering (including reflow and wave). Depending on the chosen reflow process (single, double…), it is necessary to use a PCB with appropriate mechanical characteristics, especially one with suitable Tg. 

What is Tg?

Tg (glass transition temperature) is the temperature value that guarantees the mechanical stability of the PCB during operational life time of the PCB, it refers to the critical temperature at which the substrate melts from solid to rubberized liquid, we called the Tg point, or melting point for easy to understanding. The higher the Tg point is, the higher the temperature requirement of the board will be when laminated, and high Tg board after laminated will also be hard and brittle, which benefits for next process such as mechanical drilling (if any) and keep better electrical properties during use.

The glass transition temperature is hard to be measured accurately in considerate many of factors, as well as each material have its own molecular structure, therefore, different materials have a different glass transition temperature, and two different materials may have the same Tg value even they have different characteristics, this enable us to have an alternative choice when the needed material is out of stock.

Features of High Tg materials

  • Better thermal stability
  • Good resistance to moisture
  • Lower thermal expansion coefficient
  • Good chemical resistance than low Tg material
  • High value of thermal stress resistance
  • Excellent reliability

Advantages of High Tg PCB

In general, a normal PCB FR4-Tg is 130-140 degrees, the medium Tg is greater than 150-160 degrees, and high Tg is greater than 170 degrees, High FR4-Tg will have better mechanical and chemical resistance to heat and moisture than standard FR4, here are some advantages of high Tg PCB for your reviewing:

  1. Higher stability: It will automatically improve the heat resistance, chemical resistance, moisture resistance, as well as stability of the device if increasing the Tg of a PCB substrate.
  2. Withstand high power density design: If the device has a high power density and a fairly high calorific value, then high Tg PCB will be a good solution for heat management. 
  3. Larger printed circuit boards can be used to change the design and power requirements of the equipment while reducing the heat generation of ordinary boards, and high Tg PCBS can also be used. 
  4. Ideal choice of multi-layer and HDI PCB: Because multi-layer and HDI PCB are more compact and circuit dense, it will result in a high level of heat dissipation.  Therefore, high TG PCBs are commonly used in multi-layer and HDI PCBs to ensure the reliability of PCB manufacturing.

When do you need a High Tg PCB?

Normally to ensure the best performance of a PCB, the maximum operating temperature of the circuit board should be about 20 degrees less than the glass transition temperature. For example, if the Tg value of material is 150 degrees, then the actual operating temperature of this circuit board shouldn’t more than 130 degrees. So, when do you need a high Tg PCB?

  1. If your end application requires to bear a thermal load greater than 25 degrees centigrade below the Tg, then a high Tg PCB is the best choice for your needs.
  2. To make sure the safety when your products require an operating temperature equal or greater than 130 degrees, a high Tg PCB is great for your application.
  3. If your application requires a multi-layer PCB to meet your needs, then a high Tg material is good for the PCB.

Applications that require a high Tg PCB

  • Gateway
  • Inverter
  • Antenna
  • Wifi Booster
  • Embedded Systems Development
  • Embedded Computer Systems
  • Ac Power Supplies
  • RF device
  • LED industry

Best Tech has rich experience in manufacturing High Tg PCB, we can make PCBs from Tg170 to maximum Tg260, meanwhile, if your application need to use under extremely high temperature like 800C, you’d better use Ceramic board which can go through -55~880C.

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