Indice dei contenuti
Negative vs. Positive Photoresist in PCB Manufacturing: Key Differences Explained
Etching is a critical process in printed circuit board (PCB) production that provides conductive paths by selectively eliminating excess copper from the board. Two of the most common methods are negative photoresist and positive etching. These are two fundamental photolithographic processes used to transfer a schema del circuito onto a copper-clad board.
Even though both processes yield comparable end products, they operate differently, have varying sensitivity and mechanical strength, which makes their use a crucial part in several electronic designs. Choosing the right method is crucial for achieving the desired accuracy, yield, and cost-effectiveness for your PCB.
This post will serve as your complete guide about negative and positive photoresist, explaining what each process is, how they work, and how to decide which one is best for your application.
What Is the Negative and Positive Photoresist Technique?
Negative etching makes use of a negative photoresist, the portions of which are exposed to UV radiation, hardened to resist the copper, and the unexposed portions that get dissolved, while positive etching makes use of a positive photoresist, the portions exposed to UV radiation being soluble, such that the copper underneath gets dissolved.
The following video briefly introduces the process of photolithography. Through the video, you will have a better understanding of the photolithography process.
How Do Negative and Positive Etching Work?
Etching is a process of controlled removal of unwanted material from a surface to produce detailed patterns, typically used in the production of PCBs.
Through selective protection of regions with a photoresist and exposure of other areas to chemicals, etching produces the desired traces of a circuit. The process can be done through negative or positive photoresists, each taking distinct steps to produce accurate and long-lasting patterns.
Positive Etching
The mask used is a positive image of the circuit—meaning the black lines on the film represent the copper traces that will remain.
UV light passes through the clear regions of the film, and illuminates the photoresist.
During development, this exposed resist dissolves.
The etchant removes the copper that is now uncovered (which was exposed to light).
The final copper pattern matches the opaque (black) parts of the original film.
Negative Etching
The mask used is a negative image of the circuit—meaning the clear parts of the film represent the copper traces that will remain.
UV light passes through the clear parts of the film, exposing and hardening the photoresist.
During development, the unexposed resist is removed.
The etchant removes the copper that is now uncovered (which was not exposed to light).
The pattern of copper that remains is identical to the clear regions of the original film.
Comparative Analysis of Negative and Positive Photoresist
The differences make it easier for designers to select the most appropriate method based on the needs of the project, either in terms of durability, cost, or being precise. The changes between the two etching procedures are explained below.
Sensitivity
Since negative photoresist is less UV light sensitive, it is easy to process it for larger production without needing highly precise instruments. This results in more tolerance and less error, and is compatible with typical PCB designs where ultra-high precision is not necessary.
High UV sensitivity in positive photoresist ensures fine patterns are generated within high-density circuits. Although this process needs controlled exposure and manufacturing protocol, this precision is a must for high-tech electronics that need high sensitivity as well as micro-scale accuracy.
Risoluzione
Negative photoresist gives moderate resolution, which is sufficient for normal circuit designs but is not capable of very fine or dense traces. Although it has low resolution, it is sufficient for most industrial and consumer electronics applications.
Positive photoresist may produce very tiny traces and complicated circuit designs. This functionality is necessary for miniaturised PCBs, HDI boards, and other high-density devices.
Resistenza meccanica
Negative photoresist is associated with improved copper adhesion, physically stable tracks that are resistant to thermal and physical stress. Its mechanical strength makes it especially suited to vibrated boards, handled repeatedly, or operated at high temperatures.
Positive photoresist, though precise, leaves finer scratches with reduced mechanical stress and handling strength. While the technique is capable of fine detail, handling and assembly must be undertaken carefully so it will not be destroyed, especially in boards having very thin copper layers.
Pros and Cons
Both these photoresists comes with their advantages and disadvantages. Some of the common ones have been highlighted here in this table:
Photoresist Type | Pro | Contro |
Negative Photoresist | 1. Less expensive and cost-effective for mass production. 2. Simpler to process on the shop floor. 3. High mechanical strength and reliability. | 1. Lower resolution. 2. Not possible to create very fine or detailed designs. |
Positive Photoresist | 1. Positive photoresist is extremely accurate and suitable for high-density schematics. 2. It is possible to make ultra-fine features and complex patterns. | 1. More delicate than negative etching. 2. Higher fabrication cost. 3. The process requires stringent process conditions. |
Esempi
Negative photoresist occurs in industrial and automotive boards, whereas positive photoresist occurs in avionics, medical, and HDI systems.
Negative Photoresist
- Elettronica per autoveicoli: Engine management boards, power systems, and control units.
- Industrial PCBs: Power supply boards, heavy machinery controllers, and motor drivers.
- Elettronica di consumo: Mass-produced appliances where longevity is a concern, refrigerators and televisions.
Positive Photoresist
- Dispositivi medici: Positive photoresist is utilized in monitoring equipment, wearable devices which require compact design, and it is also used in medical imaging systems.
- Avionics: In aviation machines and devices, this method is used for navigation devices and communication modules.
- PCB HDI: Smartphones, tablets, and wearable devices have high-density circuit layouts.
Negative vs. Positive Photoresist: Comparison Table
The following table summarizes the comparison of the above components.
| Caratteristica | Negative Photoresist | Positive Photoresist |
| Sensitivity | Easier to control and not affected by UV light. | Very sensitive, allows for fine designs, but needs attention in handling. |
| Risoluzione | Moderate; suitable for regular boards. | High, can handle complex layouts and micro-thin traces. |
| Resistenza meccanica | It is tough and resistant to physical and thermal stress. | fragile traces that are less resistant to stress. |
| Pros and Cons | Restricted in fine details, but strong and inexpensive. | Expensive but very precise. |
| Esempi | General electronics and industrial control boards are two examples of standard. | medical equipment, mobile phones, and aerospace electronics. |
How to Choose Between Negative and Positive Photoresist
Choosing a correct etching method depends on the type of application, sensitivity of the instrument, resolution, and several other factors. Here’s a rundown of how to choose the correct method.
When to use Positive Photoresist:
- Best for obtaining precise accuracy and dense patterns of features
- Most suitable for microelectronics, high-density interconnect boards, and small devices.
- Most appropriate where structural integrity is compromised to a neat, space-saving look.
When to use Negative Photoresist:
- When designing with thicker copper weights and greater mechanical resistance, this process is recommended.
- Best suited for high-volume productions or cost-saving programs
- Widely used in power management board designs, motor systems, and industrial electronics.
For most commercial PCB fabrication houses today, positive photoresist is the industry standard for its superior precision and consistency. However, negative resist is still employed in schoole and by hobbyists, since it is cheaper and simpler to handle.
Conclusione
Thus, negative photoresist is most suitable for power electronics and industrial use since it is robust, inexpensive, and can handle heavier copper. On the other hand, positive photoresist is the most suitable for miniaturized, high-density boards found in current devices due to its high resolution and fine features.
Both etching processes are utilised in Produzione di PCB, depending on the mechanism, sensitivity, mechanical integrity, and cost. Generally, the choice of photoresist is dependent on a compromise between durability and accuracy to meet the application’s unique needs.
Contatto FS PCBA for more PCB-related help and guidance.
Domande frequenti
The environment and human health are harmed by the toxic materials used in PCB etching. Chemical recycling and the use of biofluids could be promoted during the etching process to allay these worries.
Sustained agitation maintains even etching and prevents over-etching as well as under-etching in a PCB. Increased temperatures, on the other hand, accelerate the etching process but can also reduce etching uniformity.
Etching chemicals release vapours which cause serious threat to health-related dangers. This is why Proper ventilation protects the home against the harmful effects of vapours and chemicals released during the etching process through outflow of gases.
Richiedi un preventivo
Blog correlati
Table of Contents How to Read a Circuit Board: A Complete Step-by-Step Guide for Engineers and Technicians (2026) Printed Circuit Board Assemblies (PCBAs) form the
The Ultimate Guide to WiFi Extenders: Technology, Market Trends, and PCBA Manufacturing Insights Think about this: you are conducting an important video conference, and then
Table of Contents Voice Assistant PCBA: MEMS Microphone Array Layout & Echo Cancellation Guide In today’s smart home hubs, AI edge devices, vehicle infotainment and
Table of Contents How to Generate PCB Gerber Files: A Complete Walkthrough for Altium, KiCad, and Eagle This article was originally published in Aug 2023
Table of Contents High-Speed Serial Bus (GMSL/FPD-Link) Layout for ADAS Controller PCBA The data architecture of the vehicle is changing considerably with the evolution of
Table of Contents Automotive-Grade Manufacturing and Thermal Cycling Testing of ECU (Engine Control Unit) PCBA Today’s automobile is more than a mechanical device; it’s a