The Benefits of Using SMT Synthetic Stone or Aluminum Alloy for Reflow Carriers

With the advancement of technology, electronic products are becoming thinner and more compact. Consequently, electronic components are also getting smaller, and even the thickness of printed circuit boards (PCBs) is decreasing. The thinnest PCB Workingbear has seen is 0.4mm. Such thin PCBs are prone to deformation or warpage due to the high temperatures result in uneven thermal stress while go through SMT reflow oven, which can even cause components to fall off inside the reflow oven.

To overcome the issues of PCB deformation and component detachment, smart engineers came up with the idea of using reflow carriers/templates to support the PCBs and minimize deformation. PCB deformation is largely caused by the high temperatures softening the FR4 material, so finding a material with the following characteristics can serve as a suitable reflow carrier:

SMT Reflow Carriers Must Have the Following Material Characteristics:

  • The softening deformation temperature should be above 300°C, allowing for repeated use without deformation.

  • The material should be as inexpensive as possible and mass-producible.

  • The material should be machinable.

  • The material should be lightweight.

  • The material should have low heat absorption.

  • The material should have minimal thermal expansion and contraction. Synthetic stone’s CTE is about half that of aluminum alloy.

Advantages and Disadvantages of Using “Aluminum Alloy” and “Synthetic Stone” for SMT Reflow Carriers

In the past, we almost exclusively used aluminum alloy (and sometimes high carbon steel or magnesium alloy) to make SMT reflow carriers. While aluminum alloy is lighter than regular metals and strong enough, it’s still somewhat heavy for the operators on the production line. Additionally, aluminum alloy tends to absorb heat, requiring operators to wear heat-resistant gloves or wait for a cooling period before handling the carriers, making the operation somewhat inconvenient.

In recent years, a new material called “synthetic stone” has gradually become widely used in SMT reflow carriers, replacing aluminum alloy trays. This material is essentially a compound made by pressing high-temperature-resistant glass fibers. It can withstand temperatures above 340°C and can be machined using CNC. It has a certain hardness, is not easily deformed, and absorbs less heat compared to aluminum alloy, allowing it to be handled immediately after passing through the reflow oven. The low heat absorption also offers other benefits, making it easier for engineers to control the reflow oven’s temperature to achieve optimal soldering quality.

Related Reading: SMT Reflow Soldering Temperature Profiles Explanation and Precautions

The cost of this synthetic stone is also cheaper than the increasingly expensive aluminum alloy. However, synthetic stone is less durable than aluminum alloy and can generally be reused for about 10,000 reflow cycles.

Benefits of Using Reflow Carriers:

  • Reduces PCB deformation caused by high temperatures in the reflow oven.

  • Can support thin PCBs or FPCBs (flexible printed circuit boards) during processing and reflow.

  • Can support irregularly shaped PCBs during processing and reflow.

  • Can carry multiple PCBs through the oven at once, increasing production volume.

▼ The cross-section of synthetic stone shows layers of chemical fibers pressed together.
 The cross-section of synthetic stone shows layers of chemical fibers.

▼ Machinable synthetic stone can be CNC-machined into desired shapes and structures, comparable to aluminum alloy.
Machinable synthetic stone can be CNC-machined into desired shapes and structures, comparable to aluminum alloy.


After a period of validation, it appears that “synthetic stone carriers” are gradually being phased out or seeing stagnant growth. According to feedback from production line workers, using “synthetic stone” can cause skin irritation, possibly due to the material shedding dust and particles. Additionally, synthetic stone is less durable compared to aluminum alloy. Therefore, special consideration is needed when choosing synthetic stone for reflow carriers.

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