Rigid-flex PCBs combine rigid and flexible substrates to form versatile, three-dimensional circuits that enhance durability and design flexibility. These boards support stable component mounting and conform to complex shapes, making them ideal for aerospace, military, and other advanced applications with strict space and reliability requirements. Widely adopted across consumer electronics, medical technology, automotive systems, wearables, and IoT devices, rigid-flex PCBs allow for innovative, space-efficient designs. However, their sophisticated manufacturing processes and design complexities lead to higher production costs.
Multilayer PCB Manufacturing Processes
Step by step processes of producing multilayer PCBs, from DFM check to final inspection.
Engineering
Check all the data provided to make sure the designing of the PCB is manufacturable, functional, reliable and cost effective. Raise questions if EQ, then issue MI for production.
Material Cutting
Cut the materials into panel according to MI. Including core, Prepreg, copper foils. Tooling holes need to be drilled at this step.
Pre-treatment
Prepare for the inner layer DFR (Dry Film Resist) lamination. To increase DFR adhesion, etch the surface of copper foils by jet-scrubber, buff brushing.
D/F Lamination
Laminate Dry Film on copper foils. D/F is used as a photosensitive material for photolithography.
D/F Exposure
Expose light onto the D/F. LDI (Laser Direct Imaging), which doesn’t require mask application, is an alternative solution.
DES
Same as the following. Developing the photoresist; Etching away unwanted copper; Stripping the remaining resist to reveal the circuit pattern.
Black Oxide
Etch the surface of copper surface to ensure adhesion of coppe and Prepreg.
Lay-up
Laminate copper foils, Prepreg and black oxided core to a single panel.
Hot Press
Heat the laminated layers under pressure in a vacuum melt Prepreg by heat to multilayer PCB formation. Other processes by the following will be the same as a double-sided PCB.
Drilling
Drill on board to form through holes.
Desmear
Remove the smear and resin residues left in the drilled holes, to ensure good electrical connectivity and improve the copper plating quality.
PTH
Electroless Copper Plating, a thin layer of copper is deposited on the hole walls through a chemical process, making them conductive.
Panel Plating
Electroplating, the thin copper layer is further reinforced with additional copper through electroplating, ensuring robust and reliable electrical connections.
Pre-treatment
D/F Lamination
Laminate Dry Film on copper foils. D/F is used as a photosensitive material for photolithography.
D/F Exposure
Apply masks(films) on D/F and expose light onto the surface of copper foils. Currently, we use both ways, D/F and LDI (Laser Direct Imaging), which doesn’t require mask application.
DES
Developing the photoresist; Etching away unwanted copper; Stripping the remaining resist to reveal the circuit pattern.
O/L Inspection
Use AOI for outer layer inspection, to check for defects such as scratches, misalignments, and incomplete etching, ensuring the final board meets the required specification.
Pre-treatment
Clean and roughen the copper surface to increase the adhesion between the copper surface and solder resist
Solder Mask
Apply photo solder resist on one side then pre-baking, then printing solder resist on the other side, pre-baking, then exposure - develop - curing.
Silkscreen
Screen printing or injet printer printing the legend.
Surface Finish
Apply surface treatment according to the specification, like Lead-free HASL, OSP, Immersion Gold/ Tin/Ag etc.
Profile
CNC routing, V-scoring, or punching, to de-panel the board from working panel.
E-testing
Use Probe flying testing for prototype and small series, and E-test fixture for production orders.
FQA & FQC
Final Quality Control and Final Quality Assurance for the finished PCB.
Packing & Shipping
Packing according to the specification and deliver to wordwide customers.
High Frequency PCB Stackup
Multilayer PCB consists of core(s), Prepreg and copper foils, base on different thicknesses the detailed stackup can be vary. Leave the stackup to us if you don’t have a specific requirement. Below is a 6 layer PCB basic structure for example.
- Laminate
- Copper Plating
- Solder Mask
- Surface Finish
Multilayer printed circuit boards (PCBs) are integral components in modern electronic devices, where they provide the necessary electrical connections between various components through multiple layers of conductive copper. The structure of these PCBs is composed of several key materials, generally referred to as laminates. Here’s a breakdown of the laminates and materials used in constructing multilayer PCBs.
Multilayer PCB Materials
Multilayer PCBs are constructed from three basic material types: copper foil, prepreg and cores.
Roll of copper foil cutted into sheets to be incorporated into the outer layer of the PCB, placing it on the prepreg to create the outer layers. Typical thickness from 17um(H OZ) to 70um(2 OZ).
Prepreg (Pre-impregnated) is the most commonly semi-cured (B-stage) glass-epoxy material. It is an insulating layer without copper attached. Below are the typical prepregs for multilayer PCBs.
Types | Thickness(mil) | Resin(%) |
---|---|---|
106 | 1.8~2.5 | 69~77 |
1080 | 2.5~3.6 | 64~72 |
1086 | 3~3.5 | 61~68 |
2113 | 3.5~4.2 | 55~60 |
2116 | 4~5.4 | 53~59 |
7628 | 6.4~7.5 | 40~50 |
Fully cured (C-stage) glass-epoxy material with copper laminated to both sides. This is used for internal layers. A core is constructed from either of one sheet of prepreg (single-ply) or two or more sheets of prepreg and two layers of copper foil.
Solder mask, also known as solder resist, is a heat-resistant coating applied to selected areas of a printed circuit board (PCB) to prevent solder deposition during assembly. It protects the circuitry from short circuits, provides environmental protection, and serves as a plating resist for final finishes. The most common used Solder masks are Liquid Photoimageable(LPI) solder masks, they are popular due to their ability to accurately reproduce fine features. Alternatively, LDI (Laser Direct Imaging) Solder Mask is a new technology used in latest few years to replace traditional LPI methods, it uses laser technology to directly image the solder mask onto the PCB. Solder Mask is crucial for ensuring the reliability and longevity of PCBs by insulating conductors, preventing corrosion, and enhancing overall durability.
Solder Mask Functions
Solder masks printing is an essential process in PCB fabrication, ensuring the boards are robust, reliable, and compliant with industry standards.
Solder Mask Bridges: Creates bridges between individual solder pads and between solder pads, component holes, and vias to prevent solder from causing short circuits.
Insulates individual conductor traces to prevent short circuits and leakage currents, ensuring reliable electrical performance.
Environmental Shield: Protects copper surfaces from environmental influences such as moisture, dust, and contaminants, preventing corrosion and extending the PCB’s lifespan.
Durability: Provides a protective layer that shields the PCB from mechanical damage during handling, assembly, and operation.
Selective Coating: Acts as a resist during plating processes, allowing for selective deposition of metals on specific areas of the PCB.
Electrical Insulation: Enhances the dielectric properties of the PCB, ensuring that high-voltage areas are adequately insulated.
Markings and Labels: Allows for the inclusion of necessary markings (e.g., manufacturer, UL markings) and labels (e.g., part numbers, date codes) for identification and traceability.
Color and Finish: Available in various colors and finishes to meet specific aesthetic and functional requirements, such as improving visibility for optical inspections or enhancing the appearance of LED applications.
Component Placement: Helps in the accurate placement of components by providing clear demarcations and preventing solder from bridging unintended areas.
Heat Resistance: Withstands high temperatures during soldering processes, especially in lead-free environments, without degrading.
Regulatory Adherence: Ensures that the PCB complies with environmental regulations like RoHS, which restrict the use of hazardous substances.
Long-Term Performance: Contributes to the overall reliability and longevity of the PCB by protecting it from various environmental and mechanical stresses.
Printed circuit board (PCB) surface finishes are crucial for ensuring solderability, wire bonding, and electrical contact while protecting exposed copper circuitry. The shift towards lead-free manufacturing, driven by environmental regulations like WEEE and RoHS, has significantly impacted surface finish technology. Various surface finishes such as HASL, ENIG, ENEPIG, OSP, immersion silver, and immersion tin each have unique benefits and limitations, catering to different requirements in PCB fabrication and assembly processes.
HASL can be applied in vertical or horizontal equipment. As a pretreatment, the copper is cleaned, microetched, and fluxed. It is common for the HASL pretreatment steps to be carried out in conveyorized equipment, and then the panel to be transferred to a vertical machine that dips the individual panel into molten solder. As the panel is raised, air knives blow off excess solder. Surface finishing engineers must be aware of safety concerns, such as exposure to Pb and the possibility of equipment fires. Newer horizontal conveyorized equipment provide a safer environment as well as a more planar surface. To handle the very high temperatures of the molten alloy, equipment is manufactured from stainless steel, titanium, and other alloys. Aggressive rinsing is needed to remove flux residues, as the HASL process uses aggressive acid fluxes as compared to no clean fluxes used in other surface finish processes.
ENIG is an electroless nickel layer capped with a thin layer of immersion gold. It is a multifunctional surface finish, applicable to soldering, aluminum and copper wedge wire bonding, press fit connections, and as a contact surface. The immersion gold protects the underlying nickel from oxidation/passivation over its intended life. The nickel layer forms a diffusion barrier preventing the diffusion of the underlying copper into the gold overcoat. The nickel also strengthens the thru hole by acting as a rivet. In addition the nickel protects the copper from dissolution into molten solder at assembly. Chemically, gold is the ideal element for the external coating of PCBs. Gold does not form an oxide, so it is virtually unaffected by temperature and storage conditions that might reduce the shelf-life of other finishes. In addition, gold dissolves readily into solder, promoting superior wettability to the nickel substrate.
IPC-4552 ENIG Specification issued in 2021 has stated the electroless nickel thickness shall be 3 to 6 μm [118.1 to 236.2 μin], and the minimum immersion gold thickness shall be 0.05 [1.97 μin] at four sigma (standard deviation) below the mean; the typical range is 0.075 to 0.125 μm [2.955 to 4.925 μin]. There was no upper limit set.
OSP is very thin organic coatings used to preserve the solderability of PCB surface copper. OSP forms a complex organometallic compound with the copper surface of the PCB. The primary function of OSP is to provide a solderable surface finish, suitable for all surface mount and through-hole assembly applications and with an appropriate shelf life. The coating has demonstrated the ability to meet category 3 coating durability (shelf life of 12 months per J-STD-003 and industry data), when produced per the required vendor specifications. Some OSP coatings, may not necessarily meet this requirement, but may meet category 2 or 1 coating durability. In spite of OSP being limited to solderability preservation, OSPs are widely used worldwide on products that are not fine pitched or with high aspect ratio holes.
Immersion tin is a thin coating of pure tin, typically 0.6 to 1.2 μm thick, which protects the underlying copper from oxidation and provides a highly solderable surface. Tin is deposited using a galvanic displacement process and can be applied in vertical or conveyorized equipment. Tin boards are used primarily for solderability and have very good compliant pin connector functionality. IPC-4554 Immersion Tin Specification has specified a lower limit for thickness. The relatively thick value of 1 μm was chosen to ensure that enough virgin tin would be available at the surface for soldering after storage. It is well understood that tin forms an intermetallic (IMC) layer with the underlying copper, and that this layer continues to grow in thickness over time.
Immersion silver forms a thin immersion deposit over copper. It is a multifunctional surface finish, applicable to soldering, press fit connections and as a contact surface. It has the potential to be suitable for aluminum wire bonding. The immersion silver protects the underlying copper from oxidation over its intended shelf life. Immersion silver is a galvanic displacement process with a typical thickness range of 0.1 to 0.4 μm. The fabrication process is easy, but the coating can suffer from tarnish when left exposed after assembly in field use. Heavy tarnish can be a predictor for corrosion and functional loss.
IPC-4553 Immersion Silver Specification states: The thickness of the immersion silver deposit should be 0.12 μm [5 μin] minimum to 0.4 μm [16 μin] maximum at ± 4σ from process mean as measured on a pad of area 2.25 mm² or 1.5 mm × 1.5 mm [approximately 0.0036 in² or 0.060 in × 0.060 in]; typical value between 0.2 μm [8 μin] to 0.3 μm [12 μin].
The electrolytic nickel-gold process employs galvanic electroplating. The circuit board is placed on a rack and electrically connected to a power supply (rectifier). When immersed in a solution of metal ions, the metals are reduced as a metal coating on the PCB by the supply of electrons. The metal thickness grows in a very predictable way depending on the time, current, area plated, and efficiency of the reaction. More frequently, the coating is applied selectively in combination with another finish such as OSP. Electrolytic nickel gold is commonly used on features requiring high-force physical connections or gold wire-bonding. Several micrometers of nickel are deposited, and 0.50 to 1.5 μm of gold as the final mating surface. It is not a recommended soldering surface as the thicker gold will create embrittlement within the intermetallic phase of the solder joint. If the surface is designed as a contacting surface with multiple insertions hard gold must be used. Gold is hardened by alloying the deposit with ~3 percent of nickel, chromium, or iron. For a large number of PCBs that employ edge tab connection, the PCB is electroplated in a special plating line where only the exposed edge features are immersed into the plating cell. If the application is gold wire bonding, only soft gold (99.99) must be used. For gold wire bonding a thick gold layer ensures that the underlying nickel will not defuse all the way to the surface where it would have an adverse effect on the bonding process.
(ENEPIG) is sometimes referred to as the “universal” finish, because of the versatility of its applications. ENEPIG is suitable for soldering, gold wire bonding, aluminum wire bonding, and contact resistance. ENEPIG is formed by the sequential deposition of electroless Ni (120 to 240 μin) followed by 2 to 12 μin of electroless Pd with an immersion gold flash (1 to 2 μin) on top. It is a multifunctional surface finish, applicable to soldering and to gold, aluminum and copper wire bonding. In addition, it is also suitable as the mating surface for soft membrane and steel dome contacts, “low insertion force” (LIF) and “zero insertion force” (ZIF) edge connectors and for press-fit applications.
ENEPIG has the advantage over ENIG of being a gold wire bondable surface. ENIG is not an ideal gold wire bonding surface because over time the electroless nickel will diffuse thru to the surface along the crystal boundaries of the immersion gold and the bonding would fail. ENEPIG’s palladium layer is a diffusion barrier to the nickel, the gold remains unadulterated and is bondable with gold thickness as low as 1.2 μin or 0.03 μm. A thicker gold coating as thick as 0.1 to 0.2 μm or 4 to 8 μin would open the wire bonding operating window. Thicker gold is beyond the capability of standard immersion gold. If a thicker gold is specified then a modified immersion gold like a “reduction assisted immersion gold” would be the preferred choice.
The electroless palladium requires a reducing agent. The most commonly used reducing agent is sodium hypophosphite, this produces a phosphorus palladium deposit with 4 to 5 percent phosphorous in the deposit. The presence of phosphorous renders the palladium deposit amorphous (noncrystalline), making it the ideal diffusion barrier. Other reducing agents may produce a nonphosphorus palladium which tends to be crystalline in structure.
Top Brand Suppliers We Use
Explore our major suppliers offering top-quality products. We use top brand laminate and solder mask suppliers to guarantee quality from the source.
Technical Specifications
Explore the technical specifications of our top-quality PCBs. Discover how we ensure reliability and performance with detailed specs.
No. | Item | Standard | Advanced |
---|---|---|---|
1 | Layer Count | 2 | / |
2 | Material Vendor | ShengYi, KB, NanYa, ITEQ, isola | Panasonic, Rogers, Nelco, Arlon |
3 | Material Type | Normal FR-4, FR-4(Tg150), FR-4(Tg170), Halogen-free, CAF Resistance | Polyimide, Aluminum/ Copper-base |
4 | Finished Thickness | 0.2~5.0mm(0.005~0.197”) | 0.2~6.5mm(0.005~0.256”) |
5 | Finished Size(min) | 50 x 50mm(2 x 2") | 30 x 50mm(1.2 x 2") |
6 | Finished Size(max) | 610 x 1000mm(24" x 40" ) | 610 x 1500mm(24" x 60" ) |
7 | Trace Width/Space | 0.10/0.10mm(4/4mils) | 0.05/0.05mm(2/2mils) |
8 | Mechanical Drilling | 0.2~6.5mm(0.008"~0.256") | 0.15~6.5mm(0.006"~0.256") |
9 | Laser Drilling | / | / |
10 | Aspect Ratio | 12:1 | 20:1 |
11 | Copper Weight | 0.5~12 OZ | 20 OZ(max) |
12 | Solder Mask Color | Glossy/Matt Green, white, black, red, blue | Yellow, pink, purple |
13 | Silkscreen Color | White, black | / |
14 | V-scoring | 30° | 20°/ 45°/ 60° |
15 | Outline Tolerance | ±0.006”(0.15mm) | ±0.004”(0.10mm) |
16 | Surface Finishes | Lead-free HASL, Immersion Gold/ Tin/ Silver, Plating hard Gold, OSP | ENEPIG |
State-Of-The-Art Equipment
Our cutting-edge technology plus morden equipments to ensures unparalleled performance and reliability for all your needs.
Related IPC Standards
IPC standards provide comprehensive guidelines and requirements to ensure the quality, reliability, and performance of PCBs used in various electronic applications. These standards cover a wide range of aspects, including design, materials, manufacturing processes, testing, and quality assurance.
IPC-2221C | Generic Standard on Printed Board Design(Download a slash sheet). Published date: 12/01/2023. |
IPC-2222B | Sectional Design Standard for Rigid Organic Printed Boards(Download a slash sheet). Published date: 10/01/2020. |
IPC-2223E | Sectional Design Standard for Flexible/Rigid-Flexible Printed Boards(Download a slash sheet). Published date: 01/01/2020. |
IPC-2226A | Sectional Design Standard for High Density Interconnect (HDI) Printed Boards(Download a slash sheet). Published date: 09/01/2017. |
IPC-2228 | Sectional Design Standard for High Frequency (RF/Microwave) Printed Boards(Download a slash sheet). Published date: 10/01/2022. |
IPC-2141A | Design Guide for High-Speed Controlled Impedance Circuit Boards(Download a slash sheet). Published date: 03/01/2004. |
IPC-2315 | Design Guide for High Density Interconnects & Microvias(Download a slash sheet). Published date: 06/01/2000. |
IPC-2316 | Design Guide for Embedded Passive Device Printed Boards.(Download a slash sheet). Published date: 03/01/2007. |
IPC-4562B | Specification for Metal Base Copper Clad Laminates for Printed Boards(Download a slash sheet). Published date: 02/05/2013. |
IPC-4563 | Resin Coated Copper Foil for Printed Boards Guideline(Download a slash sheet). Published date: 02/11/2008. |
IPC-4101E | Specification for Base Materials for Rigid and Multilayer Printed Boards(Download a slash sheet). Published date: 03/01/2017. |
IPC-4103B | Specification for Base Materials for High Speed/High Frequency Applications(Download a slash sheet). Published date: 11/01/2017. |
IPC-4202C | Specification for Flexible Base Dielectrics for use in Flexible Printed Boards(Download a slash sheet). Published: 01/01/2022. |
IPC-4203B | Cover and Bonding Material for Flexible Printed Circuitry(Download a slash sheet). Published: 03/01/2018. |
IPC-4204B | Flexible Metal-Clad Dielectrics for Use in Fabrication of Flexible Printed Boards(Download a slash sheet). Published: 08/01/2018. |
IPC-FC-234A | Pressure Sensitive Adhesive (PSA) Assembly Guidelines for Flexible, Rigid or Rigid-Flex Printed Boards(Download a slash sheet). Published: 12/23/2014. |
IPC-4552B | Specification for Electroless Nickel/Immersion Gold (ENIG) Plating for Printed Boards(Download a slash sheet). Published date: 05/01/2021. |
IPC-4553A | Specification for Immersion Silver Plating for Printed Boards(Download a slash sheet). Published date: 06/16/2009. |
IPC-4554 | Specification for Immersion Tin Plating for Printed Circuit Boards(Download a slash sheet). Published date: 09/01/2013. |
IPC-4555 | Performance Specification for High Temperature Organic Solderability Preservatives (OSP) for Printed Boards(Download a slash sheet). Published date: 04/01/2022. |
IPC-4556 | Specification for Electroless Nickel/Electroless Palladium/Immersion Gold (ENEPIG) Plating for Printed Circuit Boards(Download a slash sheet). Published date: 02/05/2013. |
ASTM-B-488 | Electrodeposited Coatings of Gold for Engineering Uses. |
MIL-G-45204 | Electrodeposited Gold Plating on Metallic Surfaces. |
IPC-SM-840E | Qualification and Performance Specification of Permanent Solder Mask and Flexible Cover Materials(Download a slash sheet). Published date: 12/22/2010. |
IPC-A-600K | Acceptability of Printed Boards(Download a slash sheet). Published 07/01/2020. |
IPC-6012F | Qualification and Performance Specification for Rigid Printed Boards(Download a slash sheet). Published date: 09/28/2023. |
IPC-6013E | Qualification and Performance Specification for Flexible/Rigid-Flexible Printed Boards(Download a slash sheet). Published date: 09/01/2021. |
IPC-6018D | Qualification and Performance Specification for High Frequency (Microwave) Printed Boards(Download a slash sheet). Published date: 02/01/2022. |
IPC-TM-650 | Test Methods Manual(Download a slash sheet). Published date: 06/06/2012. |
IPC J-STD-003D | Solderability Tests for Printed Boards(Download a slash sheet). Published date: 01/01/2023. |
IPC-9252B | Requirements for Electrical Testing of Unpopulated Printed Boards(Download a slash sheet). Published date: 09/01/2016. |
Value-Added Services
From quickturn prototype PCB manufacturing to Assemblied PCB, we have got you covered.
Free DFM Check
PCB Layout optimization, EQ confirmation, to improve production yield and cost reduction.
Quickturn PCB Manufacturing
As quick as 24 Hours for Prototype PCB manufacturing, small series as fast as 5~7 days.
Prototype PCB Manufacturing
No MOQ limit, PCB Prototype as less as one single piece. Even one piece we care.
HMLV Orders
Focus on High-Mix-Low-Volume PCB Manufacturing for more than 10 years.
Components Sourcing
Hard-to-find components sourcing; NRND components substitue; global network.
Quick turn PCB Assembly
24 Hours PCB Assembly upon all components secured. Medium batch as fast as 3~5 days.
Prototype PCB Assembly
Focus on High-Mix-Low-Volume PCB Manufacturing for more than 10 years.
Turnkey PCB Assembly
From PCB Manufacturing, Parts Procurement to PCB Assembly, we have got you covered.
Frequently Asked Questions
Explore our FAQ section for clear, concise answers to your most common questions. Find the information you need quickly and easily. .
We always follow customer specification to choose the right material. From our record, CEM-1 is the most commonly used.
Single-sided PCB is the simplest PCB, it is cost-Effective, simplicity and easier to repair and troubleshoot due to the single layer of circuitry.
Single-sided PCB is only suitable for simple circuits with low component density, it's not suitable for high-speed or high-frequency applications.
Yes, but the design must consider the current-carrying capacity of the traces and ensure adequate heat dissipation. Thicker copper layers and wider traces are often used for high-current applications.
Single-sided PCBs are commonly used in consumer electronics, power supplies, industrial equipment, toys, and basic audio equipment etc.
We prefer Gerber RX-274X format, .brd, . .PcbDoc, .tgz acceptable.
For new clients, our standard payment terms are 30% advance payment and 70% before shipment. We accept various payment methods, including wire transfer and PayPal.
Single-sided PCB is always in mass production, base on the volume it usually takes 5 wds to weeks.
Single-sided PCB is easy, but we also run necessary visual Inspection, E-testings etc to ensure the quality.
We can ship to anywhere as long as there is local DHL/FedEx/UPS service there.
Get In Touch
Feel free to contact us if you have any questions, even though you have no needs at this moment.