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Steel Alloy base Allows Thick Films to Operate at High Temperatures
Posted on 28/12/2018

Introduction

Regular Metal Core Printed Circuit Boards (MCPCBs) use copper or aluminum as their metal base. The use of metal as base helps to conduct heat away from the components on the PCB, as copper and aluminum are good thermal conductors. However,such MCPCBs have to operate well below 260°C to prevent solder joints on the components from melting. For operating temperatures up to 650°C, the industry uses Thick Films withSteel Alloy as the base.

Applications of Steel Alloy Base Thick Films

Unlike MCPCBs that strive to keep components cool by conducting heat away from them, thick films with steel alloy as base are popular for providing heat in confined spaces. The steel alloy base offers superior structural properties along with a thin profile, which is suitable for a fast ramp up and down for high temperature applications.

Thick films with steel alloy base are common in applications requiring heating such as in medical and life sciences for dialysis, blood/fluid warming, temperature therapy, instrument warming, and sterilization. The aviation and transportation industry uses them for de-icing, freezer protection, battery and oil heating, and providing personal comfort. The food service industry uses thick films with steel alloy base for warming cabinets, grilling platters, heated dishware, and fryer systems. The printing industry uses them in laser print heads, 3-D printing, thermal printing, and in printer heads in commercial and industrial printing. The semiconductor industry uses thick films with steel alloy base for water heating, as wafer chuck heaters, and high temperature burn-in boards.

Advantages of Steel Alloy Base Thick Films

The major advantage of the steel alloy base is its ability to allow heating up to 650°C. Apart from this, heaters based on thick films with steel alloy base offer a low profile, are compact and lightweight, which results in fast and reliable operation. Their low mass allows fast temperature ramp up and cool down, along with power densities greater than 31 W/cm2or 200 W/in2.

With a low coefficient of thermal expansion due to the presence of the steel alloy base, thick films do not gas when operating with inorganic substances. The steel alloy base allows machining the film into complex forms and shapes.

Manufacturing Thick Films with Steel Alloy Base

Manufacturers screen-print the insulation dielectric material onto the steel alloy base, firing it at 850°C. This produces a robust substrate with high resistance to thermal shock. With normal features of porcelain-enameled steel, these substrates offer the advantages of higher processing and operating temperatures. The insulation offers an ideal area for screen-printing the thick film resistive element.

Manufacturers often incorporate temperature-sensing elements within the heating device using resistive thick film materials with positive temperature coefficient.

Manufacturers use different types of stainless steel for the substrate. For instance, EC regulations mandate the use of at least 12% Cr for the stainless steel for use in the food industry. The heating elements use both austenitic and ferritic steels, with 304 austenitic steel offering higher temperature coefficient of expansion in comparison to the TCE of 430 ferritic stainless steel types.

Conclusion

Utilising a steel alloy base has many advantages in due to its thermal profile and conductivity. To find out if your PCB design and application would benefit from the use of steel alloy as its base, feel free to contact our team at sales@pcbglobal.comto discuss.