What Is The Heavy Copper PCB Manufacturing Process?

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The Heavy copper PCB board manufacturing process requires a complex process to ensure the performance of the finished product. Printed circuit boards can be single, dual or multi-layer; the fabrication process used differing only after manufacturing the first layer. 

 The number of steps required to manufacture printed circuit boards’ correlates with their complexity. Skipping any steps or cutting back on the process can negatively impact the board's performance. 

Step 1: Design a printed circuit board PCB

The starting step of Heavy copper PCB manufacturing process is design. When it comes to PCB board design, Extended Gerber is a great piece of software as it also acts as an output format. The extended Gerber encodes all the information the designer needs, such as the number of copper layers, the number of solder masks required, and other component designation sections. 

After the design for the PCB is coded using Gerber Extended software, all the different parts and aspects of the design are checked to ensure that there are no errors.

After the designer has finished checking, the finished PCB design will be sent to the PCB fabricator. Upon arrival, the PCB design plan is checked a second time by the manufacturer, known as a Design for Manufacturing (DFM) check. Proper DFM testing ensures that the PCB design meets the minimum tolerances required for the manufacturing process.

Step 2: Evaluate Heavy copper PCB board design

Another important step of the Heavy copper PCB fabrication process involves checking the design for potential defects or flaws. An engineer reviews every part of the PCB design to make sure there are no missing components or incorrect construction. Once confirmed by the engineer, the design moves to the printing stage.

Step 3: Print the PCB design

The PCB board manufacturing process will continue once all the checks are complete, the PCB design can be printed. Unlike other plans, like architectural drawings, PCB board designs don't print out on a regular 8.5 x 11 sheet of paper. Instead, a special type of printer, called a decal printer, is used. A decal printer creates a “film” of the PCB. The final product of this “movie” looks like transparent glass – it is essentially a photo negative of the board itself.

kingford pcb

The inner layers of the PCB are represented by two ink colors:

  • Black ink:   Used for copper and circuit traces of PCB
  • Clear ink:   Indicates non-conductive areas of the PCB, like the fiberglass base

After the film is printed, they are lined up and a hole, called a registration hole. The registration hole is used as a guide to align the films later in the process.

Step 4: Print copper for the inner layers

Step 4 is the first step in the process of the manufacturer starting to produce the PCB board. After the PCB design is printed onto a piece of laminate, the copper is then pre-bonded with the laminate itself, which serves as the structure for the Heavy copper PCB. The bronze is then etched away to reveal the previous design.

Next, the laminate is covered with a photosensitive film called a contrast agent. Contrasts are made of a layer of photo-reactive chemicals that harden after they are exposed to ultraviolet light. Contrast allows technicians to get the perfect match between the photos of the design and what is printed for the camera.

When the contrast agent and laminate are lined up – using the previous holes – they receive a stream of ultraviolet light. Ultraviolet light passes through the translucent parts of the film, hardening the contrast medium. This shows that copper areas are kept as paths. In contrast, black ink prevents light from reaching unnecessary areas from hardening so that they can be removed later.

After the board has been prepared, it is washed with lye to remove any residual contrast medium. The board is then pressure washed to remove anything left on the surface and left to dry.

After drying, the only contrast agent left on the PCB was on the copper part. A technician looks at the PCB to make sure there are no errors. If there are no errors then move on to the next step of the heavy coppoer PCB manufacturing process.

Step 5: Remove the copper in the inner layer or core 

The core or inner layers of the printed circuit board need to remove more copper before PCB fabrication can continue, leaving only the required amount of copper of the board. This step may vary with time or the amount of copper etching solvent used. 

Large PCBs or those with heavier construction can use more copper, resulting in more copper having to undergo etching to remove. As a result, these boards will require additional time or solvents.

Step 6: Align Layers

After each layer of the PCB has been cleaned, they are ready for layer alignment and optical inspection. The previous holes are used to align the inner and outer layers. To align the layers, the technician places them in a type of punching machine called a puncher. The optical punch passes a pin through the holes to stack the layers of the printed circuit board.

Step 7: Check product appearance

After optical punching, another machine performs a product appearance inspection (AOI) to ensure there are no defects. Visual inspection of the product during the Heavy copper PCB manufacturing process is extremely important because once the layers are put together.

Any defects that exist cannot be corrected. To confirm that there are no defects, the AOI machine compares the PCB to the Extended Gerber design, which serves as the manufacturer's model.

Once the PCB is inspected – meaning neither the technician nor the AOI machine has found any defects – it moves on to the final few steps of the PCB manufacturing and fabrication process.

The AOI step is very important for the operation of the printed circuit board. Without it, boards could short circuit, fail to meet design specifications, or have extra copper that wasn't removed during etching that could make its way through the rest of the process. 

AOI prevents further defective boards by acting as a mid-production quality check point. The process then repeats for the outer layers once the engineers have finished shaping and etching them.

Step 8: Lamination of PCB layers

In the sixth step of the Heavy copper PCB manufacturing process, the PCB layers are all together, waiting to be laminated. Once the layers have been confirmed to be defect free, they are ready to be merged. PCB lamination is carried out in two steps: layering step and laminating step.

The outside of the PCB is made of fiberglass pieces that have been pre-soaked/coated with epoxy resin. The original baseplate was also covered in a thin layer of copper foil that now contains etchings for copper traces. Once the outer and inner layers are ready, it's time to push them together.

The clamping of these layers is carried out using metal clamps on a special press. Each layer fits the table with specialized pins. The technician performing the lamination process begins by placing a pre-coated epoxy resin known as impregnated or pre-impregnated – onto the table's alignment bath. 

A base layer is placed on pre-impregnated resin, followed by a layer of copper foil. The copper foil, in turn, is followed by multiple plastic sheets that have been pre-impregnated, then finished with a piece and a final piece of copper known as a laminate.

Once the press plate is in place, the pad is ready for pressing. The technician passes it through a mechanical press and presses the layers down and together. As part of this process, the pins are then punched through the stack of layers to ensure that they are properly secured.

If the layers are fixed properly, the PCB stack is taken to the next press, a laminating press. The laminator uses a pair of heated plates to exert both heat and pressure on the stack. The heat of the plates melts the epoxy inside the prepeg – it and the pressure from the press combine to stack the PCB layers together.

Once the PCB layers are pressed together, a bit of unpacking is required. The technician needs to remove the top press plate and the pins from it, and then allow them to pull the actual PCB out.

Step 9: Drill

Before drilling, an X-ray machine is used to locate the drilling points. The registration/guide holes are then drilled so that the PCB stack can be secured before drilling more specific holes. When the time came to drill these holes, a computer-guided drill was used to manually create the holes, using the file from the Extended Gerber design as a guide.

When drilling is complete, any additional copper left on the edges is removed.

Step 10: Plating the PCB

After the plate has been drilled, it is ready to be plated. The plating process uses a chemical to fuse all the different layers of the PCB together. After being thoroughly cleaned, the PCB is soaked in a series of chemicals. Part of this process coats the panel with a micron-thick layer of copper, which is deposited on top of the top layer and into the holes that have just been drilled.

Step 11: Outer layer image

Earlier in the Heavy copper PCB board manufacturing process (Step 4), a contrast agent was applied to the PCB panel. In Step 11, it's time to apply another layer of contrast. However, this time the contrast agent was applied only to the outer layer, as it still needed to be photographed.

 After the outer layers have been coated with the contrast agent and photographed, they will be plated in exactly the same way that the inner layers of the PCB were plated in the previous step. However, while the process is the same, the outer layers are plated with tin to help protect the outer copper layer.

Step 12: Engrave the outer layer

When it was time to engrave the outer layer for the last time, a tin guard was used to help protect the copper during the etching process. Any unwanted copper is removed using the same copper solvent as before, with tin protecting the valuable copper of the etching area.

One of the key differences between the inner and outer etching covers the areas to be removed. While the inner layers use dark ink for conductive areas and clear ink for non-conductive surfaces, these inks are reversed for the outer layers.

 Thus, the non-conductive layers have a dark ink covering them, and copper has a light ink. This lightweight ink allows the tinplate to coat the copper and protect it. Engineers remove unnecessary copper and any resistant coating left over during etching, preparing the outer layer for the AOI and the solder mask.

Step 13: Check the appearance of the outer layer product

Like the inner layer, the outer layer must also undergo a product appearance inspection. This product visual inspection ensures the grade meets the exact design requirements. It also verifies that the previous step removed all excess copper from the layer to create a properly functioning printed circuit board that will not create improper electrical connections.

Step 14: Apply the solder mask

Plates require thorough cleaning prior to application of the solder mask. After cleaning, each panel has a solder mask film and epoxy ink coating on the surface. Next, ultraviolet light shines on the board to indicate where to remove the solder mask.

After the technician removes the solder mask, the printed circuit board will be put into the oven to cure the mask. This masking provides the board's copper with an extra layer of protection from corrosion and oxidation damage.

Step 15: Skillscreen application

 Because PCBs require information directly on the board, fabricators must print important data onto the surface of the board in a process known as Skillscreen application or legend printing. This information includes the following:

  • Company ID number
  • Warning label
  • Manufacturer's trademarks or logos
  • Part number
  • Pin locator and similar marks

After printing the above information onto printed circuit boards, usually with an inkjet printer, the PCBs will be surface-finished. They then go on to the testing, cutting, and testing phases.

Step 16: Finishing the PCB board

Finishing a PCB that requires plating with conductive materials is the next step in the Heavy copper PCB manufacturing process such as the following:

  • Immersion Silver:  Low signal loss, lead free, RoHS compliant, finish can oxidize and tarnish
  • Hard Gold:  Durable, long shelf life, RoHS compliant, lead free, expensive
  • Non-Electrical Nickel Immersion Gold (ENIG):  One of the most popular finishes, long shelf life, RoHS compliant, more expensive than other options
  • Hot Air Solder (HASL):  Cost effective, long lasting, reworkable, lead free, RoHS compliant
  • Lead- free HASL:  Cost-effective, lead-free, RoHS compliant, reworkable
  • Immersion Tin (ISn):  Popular for press-fit applications, tight tolerances for holes, RoHS compliant, PCB handling can cause soldering problems, tin whiskers
  • Organic solderability preservative (OSP):  RoHS compliant, cost-effective, short shelf life
  • Non-electrostatic nickel-free palladium-infused gold (ENEPIG  ): High weld strength, reduced corrosion, requires careful handling for consistent performance, less cost-effective than non-gold or palladium-based options

Exact material depends on design specification and cost. However, the application of such finishes creates a required characteristic for PCB boards. The finishes allow an assembler to mount electronic components. The metals also coat the copper to protect it from oxidation that can occur when exposed to air.

Step 17: Check electrical reliability

After the Heavy copper PCB has been coated and cured (if necessary), a technician will conduct a battery test on different areas of the PCB to ensure functionality. Electrical testing shall  be in accordance with the standards of IPC-9252. The main tests performed are the circuit continuity test and the isolation test. Circuit continuity test checks for any disconnections in the PCB, known as "open". 

Circuit isolation test, on the other hand, checks the isolation values ​​of different parts of the PCB to check for any errors. While electrical tests mainly exist to ensure functionality, they also act as a test of how well the original PCB design has stood against the PCB board manufacturing process.

Step 18: Profile and Routing

Profiling requires fabrication engineers to determine the shape and size of individual printed circuit boards cut from the build board. This information is often found in the design's Gerber files. This profiling step guides the routing process by programming where the machine will make points on the build board.

Outbound routing, or scoring, allows for easier separation of tables. A router or CNC machine makes several small pieces along the edges of the board. These edges can cause the board to break apart quickly without damage.

Step 19: Quality Check

After grading and separating the boards, the PCB must go through one final inspection before packing and shipping. This final check verifies several aspects of the table construction:

  • Hole sizes should be consistent across all grades and meet design requirements.
  • Table dimensions should match those in the design specifications.
  • Manufacturers must ensure cleanliness so that the boards do not have dust on them.
  • The finished board should not have burrs or sharp edges.
  • All boards that fail the electrical reliability test must be repaired and re-inspected.

Step 20: Packing and Delivery

The final stage of the Heavy copper PCB manufacturing process is packaging and delivery. Packaging usually includes sealing material around the printed circuit board to keep out dust and other foreign materials. The sealed planks then go into the containers to protect them from damage during transit. Finally, they go to deliver the goods to the customer.


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