Generating a quote for rigid PCBs with standard specifications like 0.062″ thickness, FR4 material, white silkscreen, and green solder mask is easy in the rigid PCB world. This results in the ability to quote a large quantity of rigid printed circuit boards.
Generating a quote for flexible printed circuit boards or rigid-flex designs involves more intricate specifications. These can include features such as 0.005″ thickness, adhesive polyimide, coverlays, PSAs, stiffeners & white silkscreen. However, our experience shows that merely providing these specifications is not enough to furnish an accurate quote. We aim to aid our customers in their success and create top-notch components for them.
This blog post aims to highlight some of the factors that can influence the cost and delivery time during the production of flex & rigid-flex PCBs.
Flex PCBs are Different in Electronics
Flexible PCBs frequently include stiffeners, which can be composed of stainless steel, polyimide, or FR4. These boards have flexible solder masks or coverlays. They can have a stiff-flex design or a rigid-flex design, which combines rigid and flexible parts. Some flexible circuits might contain rigid stiffeners beneath the parts that don’t need to bend, whilst other flexible circuits might need to be repeatedly dynamically flexed.
Because they do not need to be able to stretch, rigid circuit boards often have a thicker construction than flexible circuit boards. While many stiff boards made of FR4 material boast a thickness of 0.062″, flexible PCBs may have a final thickness of just 0.007″. Flexible PCBs made of polyimide are easily bent. However, they frequently need to have stiffeners added for assembly, which should be included in the estimate as an additional manufacturing step.
To protect the signal circuitry, coverlays must be used. Most frequently, polyimide is used to create these protective layers. Although less flexible, a flexible solder mask can be employed in some sections of designs with tight SMTs in place of coverlays.
It’s important to clarify whether a circuit board is a straightforward flexible PCB or a more intricate rigid-flex design when getting an estimate for one. The latter includes both a flexible section made up of thin polyimide layers and a hard section.
Understanding the special needs of flexible circuit boards is crucial for getting an accurate price and ensuring a smooth manufacturing process that produces a high-quality product. Ignoring these variations can cause issues with production.
Top Factors to Consider for Flex PCB Quote
1. Special Requirements
Any unique specifications your component may have must be disclosed when requesting a quote. These extra factors may affect both the price and lead time of your component, or both.
2. Pressure Sensitive Adhesive
Your flexible PCB design might need to be mounted during assembly using double-sided tape or pressure-sensitive adhesive (PSA). As it has a better temperature tolerance during assembly, we typically use 3M 467 for individual boards and 3M 9077 for arrays at our factory. Remember that because the PSA must be manually applied, these unique requirements need additional production procedures.
3. Stiffeners
Adding polyimide stiffeners requires manual effort as well during the manufacturing process. Manual processes can lengthen the production cycle, which could result in higher costs and longer lead times.
4. Shielding
When shielding is required for the flexible circuit, the circuit board is covered with a silver ink shield (also known as a shield film). This aids in reducing electromagnetic (EM) radio frequency (RF) interference in the design, which can significantly affect the assembly’s reliability and even cause it to malfunction.
5. Controlled Impedance
In many designs, controlled impedance is important because trace pairs need to maintain uniform width and spacing to provide the appropriate resistance expressed in ohms. Controlled impedance traces need to be connected to ground planes on circuit boards that are both flexible and rigid. However, flexible circuit boards require a second polyimide sheet, called a polyimide core layer, to be positioned between the impedance layer and its reference plane layer. This additional layer is crucial to building these kinds of circuits and has an impact on both cost and construction.
6. Non-Standard Plating
When it comes to flexible circuits, the entire image—including the holes—is plated using a common design. However, certain designs call for selective plating, or “pad plating,” which mostly covers the holes and only covers the SMT portions. Boards that require great flexibility or have regulated impedance requirements benefit from pad plating.
7. Surface Finishes
HASL, gold, ENIG, and immersion silver are some of the surface finishes used on flexible circuit boards. Because it is a smaller and more flexible alternative, ENIG is now regarded as having the best flexibility during assembly. The specification of gold flash, a thin layer that offers greater flexibility than a full hard gold plate that would not bend, is essential. A gold finish may also be acceptable.
8. Flex PCB stack-ups
Circuit boards that are flexible or rigid-flex have a variety of stack-up composition possibilities. The printed circuit boards overall cost can be significantly impacted by the stack-up that is selected. One can see that a solder mask has been placed on the board’s rigid portions in the case of a 10-layer rigid-flex PCB.
It’s crucial to remember that the solder masks need not be composed of flexible material. For increased security, coverlays are placed over the board’s core flexible layers. The stack-up, which is required to join the various parts of the board together, also shows the extensive usage of glue. Prepreg is typically used to bond the flexible portions together, whereas adhesives are utilized to bond the hard multilayer sections together. When considering a flexible or rigid-flex circuit board design, having a thorough understanding of the stack-up possibilities and how they affect the pricing process is essential.
Conclusion
When seeking a Flex PCB Quote for your design, it is imperative to keep these things in mind. By giving thorough information in advance, you can be sure that you’ll get an accurate quote and delivery date for your components.
Before the quoting process, working with our engineering team ensures not only the accuracy of the estimate but also the production of a dependable and high-quality flexible circuit board. To make sure that the finished product lives up to your expectations, our staff can help you through any unique constraints your design may have.