Eurocircuits - how to make a 4-layer PCB (full version)

who are we and why have we made this film euro circuits are you repeat manufacturer of standard technology printed circuit boards or PCBs our headquarters are in the picturesque Belgian town of Mechelen and our production units are near arkin in Germany and at Egger in Hungary we specialize in providing prototype and small-batch PCBs for designers product development departments niche market electronics companies universities and research establishments we've made this film to help electronics engineering students understand how a PCB is made easily and cheaply designing boards that fit within industry standard specifications gives you two advantages you keep down the cost of your end product so that it will sell better and you improve its long term reliability so that your customers will keep on coming back to you and when you want to push the boundaries of Technology and who doesn't you can sit down with your chosen board manufacturer and discuss your requirements knowing where he is coming from what will we show you in this film in this film we will show the manufacture of a four layer multi-layer this covers all the different processes used in PCB production single and double sided boards use some of these but not all PCB manufacturers don't make each individual circuit by itself they combine several circuits on a large production panel which is much more efficient to handle through the factory a euro circuits we combine several different designs on one panel as this allows us to make small quantities of different PCBs cheaply and efficiently this we call order pooling in these films you'll see that our chosen panel has four different designs on it other manufacturers put several copies of the same design on one production panel as far as processing goes both are the same you can find out more about Euro circuits by going on our website WRO circuits calm or by emailing us at euro at Euro circuits calm frontend tool data preparation the board designer has prepared his layout on a computer-aided design or CAD system each CAD system uses its own internal data format so the PCB industry has developed a standard output format to transfer the layout data to the manufacturer this is extended Gerber or is 27 4x the Gerber files define the copper tracking layers for in the job we are following as well as the solder masks and component notations first we check that data meets our manufacturing requirements these checks are mostly done automatically we check the track widths the space between the tracks the pads around the holes the smallest hole size etc the engineer can also check and measure individual areas where he wishes once the data is verified as good he will output all the tool files needed to drive the machines that will make and test the PCB you preparing the photo tools we use laser photo plotters in a temperature and humidity controlled darkroom to make the films we will use later to image the PCBs the photo plotter takes the board data and converts it into a pixel image a laser writes this onto the film the exposed film is automatically developed and unloaded for the operator we've generated one film or photo tool per PCB layer now the films are registered with each other so that the different layers of the PCB will be perfectly aligned we do this by punching precise registration holes in each sheet of film the operator puts the film on the table of the punch and then micro adjusts the table until the targets on the film are exactly lined up with the targets on the film punch she then punches each sheet of film with the registration holes which will fit into the registration pins in our imaging equipment you print inner layers to produce the inner layers of our multi-layer PCB we start with a panel of laminates laminate is an epoxy resin and glass fiber core with copper foil pre bonded onto each side the first step is to clean the copper we print the panels in a cleanroom to make sure that no dust gets onto the surface where it could cause a short or open circuit on the finished PCB the clean panel is coated with a layer of photosensitive film the photoresist the bed of the printer has registration pins matching the holes on the photo tools and in the panel the operator loads the first film onto the pins then the coated panel then the second film the pins ensure that the top and bottom layers are precisely aligned the printer uses powerful UV lamps which harden the photoresist through the clear film to define the copper pattern under the black areas the resist remains unhardened the cleanroom uses yellow lighting as the photoresist is sensitive to UV light you outside the yellow room the panel is sprayed with a powerful alkali solution which removes the unhardened resist the panel is pressure washed and dried the copper patent we want is now covered by the hardened resist the operator checks a sample of the panels to make sure that the copper surface is clean and all the unwanted resist has been removed you can now see in the blue resist what will be the copper on our inner layer panel you H inner layers we remove the unwanted copper using a powerful alkaline solution to dissolve or xposed copper the process is carefully controlled to ensure that the finished conductor widths are exactly as designed but designers should be aware that thicker copper foils need wider spaces between the tracks the operator checks carefully that all the unwanted copper has been edged away next we strip off the blue photoresist which protected the copper image so now we have the exact pattern required the operator checks that all the photoresist has been removed you can see that uro circuits put several different designs on one production panel that way we can make small numbers of PCBs cost-effectively you register punch and automatic optical inspection the inner core of our multi-layer is now complete next we punch the registration holes we will use to align the inner layers to the outer layers the operator loads the core into the optical punch which lines up the registration targets in the copper pattern and punches the registration holes we won't be able to correct any mistakes on the inner layers once we've assembled the multi-layer so we now give the panel a complete machine inspection the automatic optical inspection system scans the board in broad strips and compares it with the digital image generated from the original design data any errors are displayed on the screen lay up and bond the outer layers of our multi-layer consists of sheets of glass cloth pre impregnated with uncured epoxy resin or pre peg and a thin copper foil the layup operator has already placed a copper foil and two sheets of pre peg on the heavy steel baseplate now he places the pre treated core carefully over the alignment pins then he adds two more sheets of prepreg another copper foil and an aluminium press plate he builds up three panels on the base plate in the same way he then rolls the heavy stack under a press which lowers down the steel top plate he pins the stack together and rolls the finished stack out of the cleanroom into a rack the press operator collects three stacks on a loader and load them into the bonding press this press uses heated press plates and pressure to bond the layers of the PCB together the heat melts and cures the epoxy resin in the prepreg while the pressure bonds the PCB together process is computer controlled to build up the heat and the pressure correctly hold it and then to cool the press down in this way we ensure a permanent bond that will last the lifetime of the PCB our board has four layers but complex PCBs for defense avionic and telecommunications applications can have more than 50 these may include sub assemblies of cause prepregs and foils drilled and plated before being assembled into the final PCB once the cycle is completed the press operator unloads the press and carefully rolls the heavy stacks into the clean room here the layup operator deepens the stack and removes the top plate he unloads each of the panels from the stack removing the aluminium press plates used to ensure a smooth copper finish the copper foil is now bonded in place to form the outer layers of the PCB you drilling the PCB now we drill the holes for leaded components and the via holes that link the copper layers together first we use an x-ray drill to locate targets in the copper of the inner layers the machine drills registration holes to ensure that we will drill precisely through the center of the inner layer pads to set up the drill the operator first puts a panel of exit material on the drill bed this stops the drill tearing the copper foil as it comes through the PCB then he loads one or more PCB panels and a sheet of aluminium entry foil the drilling machine is computer-controlled the operator selects the right drill program this tells the machine which drill to use and the XY coordinates of the holes a drills use air driven spindles which can rotate up to 150,000 revolutions per minute high-speed drilling ensures clean hole walls to provide a secure base for good plating on the hole walls drilling is a slow process as each hole must be drilled individually so depending on the drill size we drill a stack of one two three PCB panels together we can drill holes down to 100 microns in diameter to give you an idea of the size the diameter of a human hair is about 150 microns drill change is fully automatic the machine selects the drill to use from the drill rack checks that it is the correct size and then loads it into the drill head once all the holes are drilled the operator unloads the panels from the drilling machine and discards the entry and exit material during bonding excess resin from the prepreg is squeezed to the edge of the panel outside the image area this excess is now cut off on a computer-controlled profiling machine the operator loads the panel onto the bed of the machine and selects the correct program with the XY coordinates of the path for the cutter to follow the drilling machine uses the points of the drill but the profiling machine uses the specialy pattern shank the cutter Mills out the final profile for the production panel the drilled panel is now ready for plating you electroless copper deposition the first step in the plating process is the chemical deposition of a very thin layer of copper on the whole walls the operator clamps the production panels into the jigs the line is fully computer-controlled and the panels are carried through a series of chemical and rinsing baths by the overhead crane almost all PCBs with two or more copper layers use plated through holes to connect the conductors between the layers a good connection needs about 25 microns of copper on the walls of the holes this thickness must be electroplated but the walls of the holes a non-conductive glass cloth and resin so the first step is to deposit a conductive layer over the whole walls we use electroless copper that is we deposit chemically a layer of copper about one micron thick over the walls of the hole and incidentally across the whole panel this is a multi-stage process as you see from the video with washing steps between the stages we pretreat the panel then we seed the whole wall with micro particles of palladium and finally deposit the copper you image the outer layers we image the outer layers in a cleanroom to make sure that no dust gets onto the panel surface where it could cause a short or open circuit on the finished PCB the panel is first coated with a layer of photosensitive film the photoresist which is hot rolled onto the copper using a cut sheet laminator the laminated panels are collected by an automatic rack the cleanroom uses yellow lighting as the photoresist is sensitive to UV light the bed of the printer has registration pins matching the holes to the photo tools and the panel the operator loads the first film onto the pins then the laminated panel and finally the second film the pins ensure that the top and bottom layers are precisely aligned the printer uses powerful UV lamps to harden the photoresist so the photo mask is clear where we want the resist to harden and black where we don't want to resist the mylar film which protected the photoresist is now removed and the imaged panel is conveyed out of the cleanroom and through a developer which removes the unhardened resist for inner layers the copper pattern we want was covered by the resist for outer layers it is exposed ready to be plated you the operator now checks the panels to make sure that the copper surface is clean and all the unwanted resist has been removed you plating next we electroplate the boards with copper the operator loads the panels onto the flight bars he checks all the clamps to ensure a good electrical connection the panels themselves act as cathodes for electroplating and we can plate the whole walls thanks to the conductive carbon layer already deposited there the operator starts the automated plating line the copper surface of the panel's is cleaned and activated in a number of baths and then electroplated the whole process is computer-controlled to ensure that each set or flight of panels stays in each path exactly the right amount of time you can see the copper anode in their bags to ensure good conductivity through the holes we need to plate on average of 25 microns of copper on the whole walls this means that we also played 25 to 30 microns on the surface tracks so if we start with a typical 17.5 micron copper foil it will be 40 to 42 microns after processing the baths are designed to produce an even copper thickness across the panel modern chemical solutions also have good throwing power to produce an even thickness of copper right through the hole once we have plated the copper onto the board we then plate a thin layer of tin this we will use in the next step of the process when we etch off the unwanted copper foil when plating is completed the flight of panels is returned to the operator and he unloads and stacks the plated panels he then uses non-destructive testing to check a sample of each flight to ensure that the copper and tin plating is the correct thickness you H outer layers we've now plated the panel with 25 microns of copper through the hole and an additional 25 to 30 microns on the tracks and pads the copper is covered with a thin layer of tin as an etch resist now we will remove the unwanted copper foil from the surface we do this on a single continuous process line the first step is to dissolve and wash off the resist which covers the unwanted copper then we remove the unwanted copper using a powerful alkaline solution to etch away the exposed copper the process is carefully controlled to ensure that as we etch down we don't itch sideways as well this means that the finished conductor widths are exactly as designed but designers should be aware that the thicker copper foils need wider spaces between the tracks finally we strip off the thin tin coating which protected the copper image so now you can see that only designed copper pattern remains as the boards emerge from the line they are stacked automatically apply solder mask most boards have an epoxy ink solder mask printed onto each side to protect the copper surface and prevent solder shorting between components during assembly the panels are first cleaned and brush to remove any surface tarnish and then convey 'red into the yellow room each panel is given a final clean to remove any dust from the surface and loaded into the vertical Kota the coating machine simultaneously covers both sides of the panel with epoxy solder mask ink the double action ensures that the ink completely encapsulates the copper tracking typically now 35 to 40 microns higher than the surface of the panel the panels are now racked and put through a conveyorized dryer which hardens the resist just enough to allow it to be printed or tack dried the operator checks for a complete and even coating you next the coated panels are imaged for this we use a to draw UV printer the operator mounts the photo tool films on the machine and then places the panel onto the registration pins she checks that the film and the copper layer are precisely aligned mask alignment will be better than 50 microns as with the edge and the plating resists used earlier in the process the UV lamps in the machine harden the ink where the film is clear that is where we need solder mask on the finished board you the imaged panels are put on a conveyor out of the clean room and into the developer which strips off the unhardened and unwanted resist later the required resist will be further hardened or cured to provide a robust and permanent coat for this we use a conveyorized oven in the same way in which the boards were previously tack dried but first the operator checks the alignment of the solder mask on the panel and make sure that there are no traces of ink on the pads or through the holes even slight traces will compromise the solder ability of the finished PCB HS compliance surface finishes electroless gold over nickel the copper component pads and holes have been left clear of solder mask now we apply a soldier able surface finish to protect the copper until the components are soldered onto the board on this line we chemically deposit first nickel onto the copper and then a thin coating of gold over the nickel this is a chemical process needing no electrical connections the line is fully automated moving the panels through a series of tanks which clean and sensitize the copper surface and then deposit about 5 microns of nickel and a tenth of a micron of gold under the EU reduction of hazardous substances or rush legislation we cannot use LED in our finishes so we offer gold over nickel as you can see chemical silver using a similar process to deposit a sterling silver finish or lead-free hot air leveling for this the panel is lowered into a bath of molten tin as it is lifted from the bath hot air jets blast the surplus molten metal from the panel to leave an overall coating of tin about two microns thick you plated gold edge connectors for edge connectors we electroplate hard gold first the operator puts protective tape on the board above the connectors then he mounts the panel on a horizontal electroplating bath the electroplated gold is needed for edge connectors which will require repeated insertion and removal electroless gold gives good solder ability but is too soft to withstand repeated abrasion for this you require a hard electroplated gold for edge connectors we electroplate 1 to 1.5 microns of gold over 4 to 5 microns of plated nickel so if your PCB will be repeatedly inserted into a connector you should specify hard gold plate on the edge connectors when the edge connectors have been plated we will remove the tape silkscreen and cure most PCBs have a component legend to show which component goes where today we use inkjet projectors to image the legends direct from the board digital data like a conventional paper printer the inkjet printer sprays minut droplets of ink onto the panel to generate the image if a legend is needed on the second side the ink is tack dried on a conveyorized heater and the printing process is repeated the inkjet printing needs no setup previously we lost time preparing and cleaning silk screens for each legend printing that is why the legend is often called the silkscreen now we finally cure both the epoxy ink solder mask and the legend once this took 90 minutes in a batch oven now it takes less than 10 minutes using a five-stage conveyorized oven you Electrical test we electrically test every multi-layer PCB against the original board data using a flier probe tester we check each net to ensure that it is complete no open circuits and does not short to any other net the flying probe tester is easy to set up as it doesn't need to test fixture but testing every net is slow a faster test method is the acceler8 this uses four thousand tiny probes like a brush it builds an electronic map of the PCB from a preheated good board then it compares each board to be tested with its map this cuts test times by 90% you profiling the final manufacturing stage is to profile the PCBs and cut them out of the production panel for this we use computer-controlled milling machine or a router first the machine mills out any small slots or internal cutouts the cutter follows the path defined in the original tool file next the milling head automatically picks up a two millimeter cutter checks the diameter and Mills around each PCB the brush around the milling head ensures that all the dust produced is collected by the vacuum system the circuits are held in place by small bridges of material we will drill through these and then remove each separate PCB from the production panel this panel has also been V scored you v-cut scoring alternatively we can pro dividual circuits on a v-cut or scoring machine this has two cutters one above and one below the panel each cuts a v-shaped groove about 1/3 of the thickness of the material leaving a thin web holding the PCBs together scoring is especially used where the customer wants his boards delivered in a panel for assembly purposes the operator measures the depth of the cut to make sure he has set the machine to give the correct web thickness the web should be strong enough to hold the panel together but thin enough to be snapped once the panel is assembled final inspection in the last step of the process a team of sharp-eyed inspectors give each pc be a final careful check over here an inspector checks a customer's assembly panel she looks for any cosmetic defects like scratches then she measures the panel against the mechanical drawing checking hole diameters with a tapered probe if everything is okay she prints out the production release note after inspection the PCBs are vacuum sealed to keep out dirt and moisture then their bubble wrapped securely boxed sealed and shipped off to the customers throughout Europe by overnight courier the process is complete we have followed our PCB from the customer's original design to the physical circuit board on its way to him to be assembled into his finished product you

Channel: Eurocircuits

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Id: sIV0icM_Ujo

Length: 32min 17sec (1937 seconds)

Published: Tue Jan 29 2013