Electrical Engineering | PCB Design
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Electrical Engineering | PCB Design
The start step associated with a PCB manufacture is, obviously, the look. PCB manufacture and style always begins with an agenda: the designer explains a blueprint for that PCB that fulfills all of the needs as outlined. Probably the most generally-used design software utilized by PCB designers is really a software known as Extended Gerber – also referred to as IX274X.
First Step: PCB Design regards to PCB design, Extended Gerber is a superb software program since it also works being an output format. Extended Gerber encodes all the details the designer needs, like the quantity of copper layers, the quantity of solder masks needed and yet another bits of component notation. When a design blueprint for that PCB is encoded through the Gerber Extended software, all of the different parts and facets of the look are checked to make certain there are no errors.
When the examination through the designer is finished, the finished PCB design is distributed off and away to a PCB fabrication house so the PCB could be built. On arrival, the PCB design plan undergoes another check through the fabricator, referred to as a The perception of Manufacture (DFM) check. An effective DFM check helps to ensure that the PCB design fulfills, at least, the tolerances needed for manufacture.
Second Step: Printing the PCB Design
In the end the checks are complete, the PCB design could be printed. Unlike other plans, like architectural sketches, PCB plans don’t print on the regular 8.5 x 11 piece of paper. Rather, a unique type of printer, referred to as a plotter printer, can be used. A plotter printer constitutes a “film” from the PCB. The ultimate product of the “film” looks similar to the transparencies that was once utilized in schools – it’s basically a photograph negative from the board itself.
The interior layers from the PCB are symbolized in 2 ink colors:
Black And White: Employed for the copper traces and circuits from the PCB
Obvious Ink: Denotes the non-conductive regions of the PCB, such as the fiberglass base
Around the surface layers from the PCB design, this trend is reversed – obvious ink refers back to the type of copper pathways, but black and white also describes places that copper is going to be removed.
Each PCB layer and also the associated solder mask will get its very own film, so an easy two-layer PCB needs four sheets Body for every layer and something each for that associated solder mask.
Following the film is printed, they’re arranged along with a hole, referred to as a registration hole, is punched through them. The registration hole can be used as help guide to align the flicks afterwards along the way.
Third Step: Printing the Copper for that Interior Layers
Third step is the initial step along the way in which the manufacturer starts to help make the PCB. Following the PCB design is printed onto a bit of laminate, copper will be pre-glued to that particular same bit of laminate, which can serve as the dwelling for that PCB. The copper will be etched off to reveal the blueprint from earlier.
Next, the laminate panel is included by a kind of photo-sensitive film known as the resist. The resist consists of a layer of photo-reactive chemicals that harden after they’re uncovered to ultraviolet light. The resist enables technicians to obtain a right diamond necklace between your photos from the blueprint and what’s printed towards the photo resist.
When the resist and also the laminate are arranged – while using holes from earlier – they get a blast of ultraviolet light. The ultraviolet light goes through the translucent areas of the show, hardening the photo resist. This signifies regions of copper that should be stored as pathways. In comparison, the black and white prevents any light from dealing with areas that aren’t designed to harden to enable them to later be removed.
When the board continues to be prepared, it’s washed by having an alkaline means to fix remove the leftover photo resist. The board will be pressure-washed to get rid of anything left at first glance and left to dry.
After drying, the only real resist that needs to be left around the PCB is on the top the copper that continues to be included in the PCB when it’s finally sprang free. A specialist looks within the PCBs to create there are no errors. If no errors can be found, then it’s to the next thing.
Fourth Step: Eliminating the Unneeded Copper
The following stage along the way is taking out the undesirable copper. Similar to the alkaline solution from earlier, another effective chemical can be used to consume away in the copper that isn’t included in photo resist. When the unprotected copper is taken away, the hardened photo resist from earlier must be removed, too. Another solvent can be used, departing just the copper essential for the PCB.
Observe that with regards to taking out the undesirable copper out of your PCB, heavier boards may need more copper solvent or even more contact with the solvent.
Fourth Step: Inspection and Layer Alignment
After each one of the PCB’s layers happen to be cleaned, they’re ready for layer alignment as well as an optical inspection. The holes from earlier are utilized to align the outer and inner layers. To align the layers, a specialist places them on a kind of punch machine referred to as an optical punch. The optical punch drives a pin lower with the holes to set up the layers from the PCB.
Fifth Step for making PCB
Following a optical punch, another machine performs an optical inspection to make certain there aren’t any defects. This optical inspect is amazingly important because when the layers are put together, any errors which exist can’t be remedied. To verify there are no defects, the AOI machine blogs about the PCB to become inspected using the Extended Gerber design, which can serve as the manufacturer’s model.
Following the PCB has transpired inspection – that’s, neither the specialist nor the AOI machine found any defects – it moves to the last couple steps of PCB manufacture and production.
Sixth Step: Laminating the PCB Layers
At sixth step along the way, the PCB layers are altogether, waiting to become laminated. When the layers happen to be confirmed to be defect-free, they’re prepared to be fused together. The PCB laminating process is performed in 2 steps: the lay-up step and also the laminating step.
The outdoors from the PCB consists of bits of fiberglass which have been pre-drenched/pre-coated by having an epoxy resin. The initial bit of substrate can also be covered inside a layer of thin copper foil that now provides the etchings for that copper traces. When the outer and inner layers are prepared, it’s time for you to push them together.
The sandwiching of those layers is performed using metal clamps on the special press table. Each layer fits to the table utilizing a specialized pin. The specialist doing the laminating process starts by putting a layer of pre-coated epoxy resin Known as pre-impregnated or prepreg – around the alignment basin on the table. A layer of substrate is positioned within the pre-impregnated resin, adopted with a layer of copper foil. The copper foil is within turn adopted by more sheets of pre-impregnated resin, that are then completed with a bit of and something last bit of copper referred to as a press plate.
When the copper press plate is within place, the stack is able to be pressed. The specialist takes it to an analog press and presses the layers lower and together. Included in this method, pins will be punched lower with the stack of layers to make sure that they’re fixed correctly.
When the layers are fixed correctly, the PCB stack is taken to another press, a laminating press. The laminating press uses a set of heated plates to use both pressure and heat towards the stack of layers. Heat from the plates melts the epoxy within the prepeg – it and also the pressure in the press combine to fuse the stack of PCB layers together.
When the PCB layers are pressed together, there’s some unpacking that should be done. The specialist must take away the top press plate and also the pins from earlier, which in turn enables these to pull the particular PCB free.
Step Seven: Drilling
Before drilling, an X-ray machine can be used to discover the drill spots. Then, registration/guiding holes are drilled so the PCB stack could be guaranteed prior to the more specific holes are drilled. When the time comes to drill these holes, a pc-led drill can be used to help make the holes themselves, while using file in the Extended Gerber design like a guide.
When the drilling is finished, any extra copper that’s remaining in the edges is filed off.
Step Eight: PCB Plating
Following the panel continues to be drilled, it’s prepared to be plated. The plating process utilizes a chemical to fuse all the various layers from the PCB together. After being cleaned completely, the PCB is bathed in a number of chemicals. Thing about this bathing process jackets the panel inside a micron-thick layer of copper, that is deposited outrageous-most layer and in to the holes that are just drilled.
Prior to the holes are full of copper, they just actually expose the fiber glass substrate that produces the panel’s insides. Bathing individuals holes in copper covers the walls from the formerly-drilled holes.
Steps Nine and Ten: Imaging and Plating the Outer Layer
Earlier in the process (Step 3) a photo resist was applied to the PCB panel. In Step 9, it’s time to apply another layer of photo resist. However, this time the photo resist is only applied to the outside layer, since it still needs to be imaged. Once the outer layers have been coated in photo resist and imaged, they’re plated in the exact same way the interior layers of the PCB were plated in the previous step. However, while the process is the same, the outer layers get a plating of tin to help guard the copper of the outside layer.
Step Eleven: The Last Etching
When it comes time to etch the outside layer for the last time, the tin guard is used to help protect the copper during the etching process. Any unwanted copper is removed using the same copper solvent from earlier, with the tin protecting the valued copper of the etching area.
Once all the unwanted copper is removed, the PCB’s connections have been properly established and it’s ready for solder masking.
Step Twelve: Applying the Solder Mask
To make the panels ready for solder mask application, they’re cleaned. Once the PCB panels have been cleaned, an ink epoxy is applied, along with a solder mask film. The boards are blasted with ultraviolet light to mark out certain portions of the solder mask for removal.
After the unwanted pieces of solder mask have been removed, the PCB is placed into an oven and baked so that the solder mask will cure.
Steps Thirteen and Fourteen: Finishing the PCB and Silkscreening
As part of the finishing process, the PCB is plated with gold, silver, or HASL so the components are able to be soldered to the pads created and to protect the copper.
After the PCB has been gold or silver-plated, as necessary, it is silk-screened. The silk-screening process prints all of the vital information on the PCB, such as manufacturer marks, company ID numbers and warning labels.
Once the PCB has been plated and silk-screened with the correct information, it can be sent along to the final curing stage.
Step Fifteen: Electrical Reliability Testing
After the PCB has been coated and cured (if necessary), a technician performs a battery of electrical tests on the different areas of the PCB to ensure functionality. The main tests that are performed are the circuit continuity and isolation tests. The circuit continuity test checks for any disconnections in the PCB, known as “opens.” The circuit isolation test, on the other hand, checks the isolation values of the PCB’s various parts in order to check if there are any shorts. While the electrical tests mainly exist to ensure functionality, they also work as test of how well the initial PCB design stood up to the manufacturing process.
In addition to basic electrical reliability testing, there are other tests that can be used to determine if a PCB is functional. One of the main tests used to do this is known as the “bed of nails” test. During this text, several spring fixtures are attached to the test points on the circuit board. The spring fixtures then subject the test points on the circuit board with up to 200g of pressure to see how well the PCB stands up to high-pressure contact at its test points.
If the PCB has passed its electrical reliability testing – and any other testing the manufacturer chooses to implement – it can be moved on to the next step: cutting.
Step Sixteen: Cutting and Profiling
The last step of the PCB manufacturing process is the cutting and scoring of the PCB. This involves cutting out the different PCBs from original panel. There are two ways that PCBs can be cut from their original panels:
Using a CNC machine or router, which cuts out small tabs around the edges of the PCB
Using a V-groove, which cuts a diagonal channel along the sides of the board
No matter which way you use, your PCB will be able to easily come free of the construction paneling.
Usually, PCB panels have the individual boards – or larger arrays, if applicable – routed out and scored so they can be broken off of the construction board after they’ve been assembled.
Once the boards are broken off the construction board, there comes a final inspection phase:
The boards are checked over for general cleanliness to ensure that there are no sharp edges, burrs or other manufacturing hazards
Slots, chamfers, bevels and countersinks are added during the routing and fabrication process, as necessary
If possible, any shorts are repaired – the shorted boards are then re-tested using the same electrical reliability tests from above
A visual inspection can be conducted, if necessary, to ensure that boards meet industry specifications and match up to the details laid out in Gerber data: the technician can also use the visual inspection to verify the hole sizes and the physical dimensions of the PCB, if required.