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Why should we focus on TG on PCB ?
gesptechnologypcbSeptember 16, 2022 Blog 0 Comment725views

Introduction

 

Temperature fluctuations can have a substantial impact on PCBA performance, dependability, and quality. Rising temperatures, in particular, cause the PCB material to expand. resulting in mechanical strains that may develop micro-cracks . that are not detectable during final electrical tests.

As a result, the principal materials used to make PCBs have varying TG vaule of thermal expansion. In the prototype quotation, it will have an option on the PCB Tg value. Tg value will also effect the ultimate cost of proofing. due to the selection of different PCB materials.

PCB Tg In the prototyping and fabrication always encounter Tg130, TG150,TG170,TG180, Let us understand the role of Tg in the PCB industry through this article .  

  1. What is the Tg of PCB? 
  2. What doesthe type of Tg PCB? 
  3. Why we choose high tg PCB materials?
  4. What the benefit of High Tg PCB?
  5. What is the impat of Tg value in PCB processing ? 
  6. What is the difference between them? 

 

What is the Tg of PCB?

  The PCB Tg is the glass transition temperature of the board under high-temperature heat. As we all know, the board must be flame-resistant. At a certain temperature, it can not burn, only soften. This time, the temperature point means the glass transition temperature (Tg point). This value cares about the stability of the PCB board. The higher the Tg value, the better the temperature resistance of the board, especially the high Tg used in the lead-free tin spraying process.  

FR4 PCB TG

FR4 PCB TG

 

Classifications of FR4-Tg PCB

 

General Tg 

  The general test sheet is 130 degrees or more. Generally, we call it the Tg130 PCB.

 

High Tg

  High Tg is generally greater than 170 degrees and is usually called Tg170 PCB, Tg175 PCB, or Tg180 PCB.

 

Medium Tg PCB

  TG is about greater than 150 degrees, so we call it Tg150 PCB. High Tg PCBs are mostly used in high multilayer printed circuit boards (10 layers). automobiles, packaging materials, and buried substrates. precision instrumentation for industrial control, routers, and other fields. The higher the Tg value, the more heat resistance, and humidity resistance. chemical resistance, stability resistance. and other characteristics of the printed board have increased at the same time.   https://www.youtube.com/watch?v=5lH_Xt2KUjA&t=8s

The Benefits of High Tg PCB

 

  • Increased stability: if the Tg of the PCB substrate higher. It will improve heat resistance and chemical resistance automatically. The device’s moisture resistance and stability
  • Withstand high power density design: If the device needs to have a high power density. High Tg PCBs are a good choice for high heat dissipation requirements.
  • Ideal for multilayer circuit boards and HDI PCBs. because they are more compact and circuit-dense. It will result in a significant amount of heat dissipation. As a result, high Tg PCBs are typically used for multilayer applications. and HDI PCB to ensure PCB manufacturing reliability.
HIGH-TG-PCB

HIGH-TG-PCB

 

Methods of Detection Tg Vaule

  The Scanning Calorimeter Method ( DSC: Differential Scanning Calorimeter Mechanical Analysis ),   Thermomechanical Analysis ( TMA: Thermal Mechanical Analysis )   Dynamic Mechanical Analysis ( DMA: Dynamic Mechanical Analysis).   The DMA curves are more visible in detail when compared with DSC. also fine structures such as the secondary transformation of the material can be observed. Both testing methods controlled by temperature procedures such as temperature rise. temperature drop, and constant temperature. and both are thermal analysis techniques that can compare Tg values.

However, TMA is only applicable to a single Tg value, and the test results are lowstructuresthe   As the results are mostly for reference when we use TMA to test Tg, which is not used as a theoretical basis. The information obtained by the DSC method to characterize the thermal properties and composition of the sample. which is the change of thermal properties, and Tg reflects the material in the thermal action.   The information obtained by the DSC method is to characterize the thermal properties and composition of the sample. which is the change of thermal properties. Tg reflects the change in the internal quality of the material under the effect of heat. which is a guideline for the material preparation process.  

Tg Value and PCB Reliability

  PCBs made of high Tg plates perform better than ordinary Tg. and medium Tg PCBs in terms of stability and reliability.   1. High heat resistance: reduces warpage due to temperature. which can reduce the PCB in hot melt welding and thermal shock pad warpage.   2. Low coefficient of thermal expansion (low CTE). This reduces the thermal expansion caused by the hole corner copper fracture. especially in the eight layers or more than eight layers of PCB boards. The reliability of the plated through-hole performance is better than the ordinary Tg PCB board.   3. Excellent chemical resistance, in the wet process of chemical immersion. Its performance is still better.    

The Impact of Tg Value in PCB Processing

  The Tg of PCB in the process is affected by the following aspects. First of all, open the baking board. The temperature should not be too high. The temperature of 10 °C is better than the temperature of 10 °C. (Such as general High Tg high-speed material at 170 °C for 4 hours conditions baking board). This is mainly to release the residual internal stress in the board, and to remove water. to promote the resin in the board material to further cure.  Secondly, after the baking, brown the board after the wet process of drug soaking. The board material absorbed a certain amount of water.

If the water residue in the board will affect the quality of the pressboard. The board material Tg value affects the browning up to 120 °C for 1 hour. The PP of the press board absorbs a certain amount of water during storage. The water residues in the polymer molecular chain is extremely difficult to discharge in the hot press. If not dehumidified, the press board is very easy to burst. delamination and other bad press board defects. so it will also affect the size of the Tg value, must be dehumidified before the press.  

The Difference betweenTG130/TG150/TG170/TG180

  The Tg value is the critical temperature at which the substrate melts from a solid state to a rubbery fluid. When the temperature of the FR-4 substrate’s binder epoxy resin is lower than Tg. the material is in a rigid “glass state”. When the temperature is higher than Tg. the material will show a rubber-like nature with softness. as long as the resin does not decompose. When the temperature becomes below the Tg value, it returns to its glassy state.

DIFFERENCE TG130 TG170

DIFFERENCE TG130 TG170

 TG130 VS. TG170

The higher the Tg value of all the plates, the better the temperature resistance of the plates. High Tg application is more common, especially in the lead-free tin spraying process.   The general Tg of the plate is 130 degrees or more. High Tg is generally greater than 170 degrees. and medium Tg is about greater than 150 degrees. High Tg sheets are mostly used in high multilayer printed circuit boards (10 layers). automobiles, packaging materials, and buried substrates. precision instrumentation for industrial control, routers, and other fields. increased the Tg of the board, the heat resistance, humidity resistance, and chemical resistance. stability resistance and improved other characteristics of the printed board. accordingly, i.e., the higher the reliability.  

Conclusion

  However, the high Tg value of the substrate is more rigid and brittle than low Tg substrates. This affects the productivity of the PCB process, especially the drilling process. If the board needs to be very dense. and the spacing between the holes is also very small. we recommended the use of a high Tg value plate. Because the ordinary Tg hole spacing design can not be less than 12 mils, while the Tg can not be less than 10 mils. High Tg value because the plate is too hard. The plate glass cloth, coupled with the new drill nozzle.

It can effectively improve the plate glass cloth in the drilling of strains to prevent the wick effect.   So, in general, the higher the Tg value, the better the temperature resistance of the sheet. The less severe the deformation of the sheet, the better the warpage. However, because of the high Tg value, it means that the temperature requirement of the board in the substrate is also high.

The pressed board will be harder and more brittle. which will affect the quality of the mechanical drilling and the electrical properties of the board.   At GESP Technology, Professional PCB one-stop service. Our ongoing goal is to help every client to go to the market as quickly as possible. and occupy more competitive advantages through our supply services. To supply zero-defect PCBs while meeting the demands of customers to achieve sustainable production    

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