FR-2 PCB Manufacturing

The Cheapest Board That Will Do the Job

Not every product needs a high performance substrate. A television remote control, a battery operated toy or a simple light strip has modest electrical demands, a benign environment and an overwhelming requirement for low cost. For those products the paper phenolic material known as FR-2 remains the sensible choice, and it is still produced in very large volumes for exactly that reason.

Knowing what FR-2 can and cannot do is the key to using it well, because the material has hard limits that are easy to exceed by accident.

What the Material Is

FR-2 is a flame retardant grade of board made from a paper base impregnated with phenolic resin. The designation follows the international standard for flame retardant materials, and the number identifies the specific material class, in this case a paper and phenolic construction. It is used almost exclusively for single sided boards, which follows directly from the material’s mechanical behaviour.

The substrate meets the standard flammability requirement, has a moderate dielectric strength suited to low frequency circuits, and is easy to cut and drill, which is part of why it is economical to process. Its temperature capability is limited to around one hundred and five to one hundred and thirty degrees Celsius, and its moisture absorption is higher than that of a glass reinforced material.

Where FR-2 Performs Well

Cost is the obvious advantage: it is among the least expensive substrates available, and the processing is simple, so the finished board is inexpensive in both material and labour. It is easy to machine, which suits the simple shapes and the high volume panelisation that low cost products use, and it has adequate insulation resistance for basic circuits.

Supply is not a constraint, because the material is widely available and most fabricators can process it. For a product whose electrical function is simple, whose environment is dry and moderate and whose life is measured in a few years rather than a decade, FR-2 delivers what is required at the lowest available price. Our notes on PCB manufacturing describe the process.

Where It Cannot Be Used

The limitations are the mirror image of the advantages. The temperature capability rules it out anywhere near a heat source, which means it cannot carry a power device, a high brightness light source or a board that will be reflowed at the temperatures that lead free soldering requires without careful process control. The mechanical strength is low, so a board that will be flexed, dropped or subjected to vibration is a poor fit. The moisture absorption is higher, so a humid environment degrades the material’s electrical performance over time.

Most importantly, FR-2 supports only a single sided design. A product that needs two layers of routing, or a ground plane, or any of the electrical benefits that a multilayer stack-up provides cannot use it. That constraint alone rules FR-2 out of most modern electronics, because even simple products now have an integrated circuit and a radio that benefit from a proper ground reference.

FR-2 Compared With FR-4

FR-4 uses a woven glass fabric with an epoxy resin rather than paper with phenolic. The consequences are a higher temperature capability, around one hundred and fifty to one hundred and eighty degrees Celsius depending on the grade, much better mechanical strength, lower moisture absorption, better dimensional stability and the ability to support double sided and multilayer construction.

The trade is cost: FR-4 is more expensive, and it requires more careful processing. The decision is therefore straightforward in principle. If the product is a simple, dry, low temperature, single sided design, FR-2 reduces cost without a functional penalty. If any of those conditions fails, FR-4 is the correct choice and the additional cost is buying reliability rather than performance. Our notes on quality management describe how the material choice is fixed with the customer.

Manufacturing

The process for an FR-2 board is similar in outline to a single sided FR-4 board. Copper foil is applied to one side, the pattern is transferred by exposure and development, the unwanted copper is etched away, the holes are drilled, and a solder mask and legend may be printed. A surface finish is applied, commonly hot air levelling or an organic solderability preservative, and a silkscreen legend may be added.

Because the cost target dominates, the simpler process options are usually chosen: a basic finish, a minimal mask, and no unnecessary processing steps. The material’s low temperature tolerance also means that the soldering process has to be controlled to avoid blistering or delamination, which is an assembly consideration rather than a fabrication one but has to be agreed between the two. Our PCB assembly group handles the assembly side.

Applications

Remote controls, simple lighting products and light strips, calculators and clocks, toys, basic audio devices and other simple battery operated products are the classic applications. They share a common profile: low component count, low frequency operation, no significant heat generation, a dry indoor environment and a price point where the substrate cost is a meaningful part of the bill.

Selection Questions

Four questions decide the material. Does the design need more than one routing layer? Will the board be exposed to temperatures above about one hundred and thirty degrees? Will it see mechanical stress, and will it be used in a humid environment? Will it be expected to last more than a few years?

If the answer to all four is no, FR-2 is a reasonable choice and will save money. If any answer is yes, the saving from FR-2 is likely to be paid back in returns. Our PCB capabilities page describes the material range available.

Cost and Availability

The unit price of an FR-2 board is very low, particularly at volume, because both the material and the processing are inexpensive. Minimum order quantities are also low because the tooling is simple, which makes the material accessible to small production runs as well as to large ones.

The finish, the board size and the surface treatment all move the price within its narrow band, but the material is inherently cheap and will remain the lowest cost option for single sided work.

Environmental Note

FR-2 is not a biodegradable material and is not considered an environmentally preferable substrate, so products that use it should be designed for responsible disposal or recycling at end of life. Where a product’s environmental requirements are strict, a different material may be preferable even at higher cost.

FAQ

Can FR-2 be used for a double sided board? No. The material supports single sided construction only, which rules out double sided and multilayer designs.

Is FR-2 suitable for a household appliance? Only for a non critical, low power, low heat application such as a remote control or a simple lighting product.

Can components be soldered to FR-2? Yes, but the soldering temperature has to be controlled because the material delaminates or blisters if it is overheated.

Does FR-2 meet the flame retardant requirement? Yes, it is a flame retardant grade and meets the standard flammability classification.

When should FR-4 be used instead? Whenever the design needs two or more layers, higher temperature capability, mechanical strength or lower moisture absorption.

Conclusion

FR-2 is the economical substrate for simple, single sided, low temperature products, and it remains the cheapest option for that class of design. Its limitations are real and easy to exceed, so the material choice should be made from the electrical, thermal and mechanical requirements rather than from the price alone.