PCB Prototyping Process:
The use of PCBs in electronic devices and instruments is of great importance. PCBs are the core of any electronic product. In other words we can say that an electronic product is nothing more than a highly qualified and complex PCB with different functional sections like power supply, processor, memory, display etc implemented using SMT and THT electronic components. While the market of electronic industry is booming day by day, the customers are demanding more advanced functions in their product while keeping the dimensions of PCB as small as possible and making the product handy. Hence design engineers are constantly improving their “circuit design” to optimize the design by using smaller components, assembling components on tighter PCB board space and improving the battery life of electronic products. There countless electronic circuit designs a team of RnD and DnD can make and then verify their designs through simulation and prototyping.
Design Verification through Simulation:
The first step in order to verify the authenticity of your circuit design is to do a simulation of your circuit. There are numerous software available that are free of cost and some are licensed to run simulation to verify the design parameters like voltage, current, frequency, power, signal analysis and other features, to test functionalities of your circuit and perform built in simulation analysis like transient analysis, DC operating point analysis and other types of simulation analysis can be run in order to verify your circuit design. Simulation software like Multisim, LT-Spice, P-Spice, Logisim and others are commonly used.
Circuit Design Prototyping:
The easiest way to do a prototyping is to use a Bread-Board to assemble your THT components and use jumpers to test your circuit performance by using commonly available lab instruments like Digital Multimeter (DMM), Oscilloscope, Function Generator, DC Power Supply. But note that only THT (Through Hole) components can be used in breadboard assembly and not SMT. There is a free software name “Fritzing” that is very helpful in making a graphical view of arrangement of components on breadboard prototyping.
Another method is used by soldering components on vero-board. Here also the components soldered are THT but vero board prototype is more solid than breadboard and has no lose connections like in breadboard.
However the two methods discussed are not very professional and mostly these are methods used by hobbyists and students. Larger OEM companies while doing RnD on their products come up with circuit design, prefer to fabricate few “prototype PCBs”. The PCB prototyping means that you hire a CEM “Contract Electronic Manufacturer” to develop few 5-10 pcs of prototype PCBs and then you do tests and run different programs on your PCB to check its functionalities.
Purpose of PCB Prototyping:
1- To make sure your circuit design works according to requirements.
2- To perform various types of test on prototype PCB to check its functionalities cost effectively.
3- To check the behavior of PCB under various environmental conditions like temperature, pressure etc
4- To avoid loss of significant amount of monetary investment and time in mass production of PCBs due to faults in circuit design. It is highly recommended to go for prototype PCBs when your design is novel or you create some modifications in existing design so you can catch any flaw in your design at early stage before going into production run.
PCB Prototyping/Fabrication at Rayming PCB:
We at Rayming PCB are capable to offer our customers any kind of prototype circuit boards they require. No matter it is single or double-sided FR4 boards or very high technology blind and buried via boards, boards made with unique materials, metal core boards, heavy copper boards, burn-in boards, rigid-flex PCB and flex PCB, they will be able to get them from us.
By networking with fully qualified PCB manufacturing and assembly facilities, including HDI PCB, we can provide printed boards as quickly as in 12 – 24 hours, depending on the technologies required, and assemble them in as quickly as 24 hours.
PCB Assembly at Rayming:
PCB prototyping is our specialty service no matter it is PCB fabrication or assembly. Our expert engineers will check and test your layout to make sure the good prototype is fabricated and assembled. With the help of our network of component suppliers and SMT assembly engineers, we make sure a quick turn around and high quality circuit board. We offer low volume circuit assembly for prototyping with DFM and DFT to avoid issues/faults in your product. We welcome you to send us your BOM and design files at firstname.lastname@example.org for inquiry and quotation. Our average lead times for assembly is 1-5 days for just PCB assembly and 10-16 days for turnkey PCB assembly.
PCB Prototyping Process:
Step-1: Know what Information is required by your CEM:
The first step in the process of prototyping the PCB is to that you as OEM/ODM know what to expect from us as your CEM. So in order to get a completely fabricated, assembled and tested and qualified PCB prototype you should send us the maximum information about your design in terms of design files on the above mentioned email address. Some of the major design information required for PCB prototyping are mentioned below.
2- Board layer stack details like board thickness,
3- Weight and thickness of copper
4- Design constraints like minimum hole size, minimum space between traces and vias, pad-pad and pad-trace clearances,
7- NC Excellon Drill files, and tool list
8- Pick and place files, assembly drawing files, 3D model details (if available)
We can convert your PCB design Gerber file into Gerber RS-274X that is the standard.
Step-2: Design your circuit
You can design your circuit by hand or by using any available EDA CAD software like ALTIUM, EAGLE, ORCAD, EAGLE, KICAD etc. This early design is usually on paper and a professional circuit layout designer can use these software to capture in any of the above mentioned CAD software
Step-3: Schematic Capture:
The next step is to capture the circuit design from paper to schematic Diagram on CAD EDA software. This step is highly important because this is the basis on which “nets” will be generated that will transport the wire connection in schematic components to PCB layout. It is important to run electrical rule check “ERC” to identify any faults at earlier stage in schematics. Any unidentified error in schematic will be replicated in PCB automatically. Hence the schematic should be checked several times before converting to PCB.
Step-4: BOM (Bill of Materials)
The BOM is also known as parts list, shows the details of components being used on circuit design. The BOM gives details of component designator, component values, description, manufacturer part number, supplier details, footprint details and quantity. The design engineer should choose components as per the requirements of the project/design and that are also cost effective.
Step-5: PCB Layout:
The most important step is the PCB layout routing. Here the design is transported from schematics along with “netlist”. The netlist will show on PCB the (connection between two components on schematics) straight lines between components. In this step the board shape and size are first defined, then the board borders are defined, then components are placed optimally on the PCB board on top, bottom or both sides. After this the components are connected/routed with each other according to the nets.
Step-6: DRC Check:
After the PCB layout is done, the DFM check i.e. DRC (Design Rule Checker) has to be run. The DRC is the checker system built in the PCB CAD/EDA software that follows the rules set by the PCB/circuit designer in the Design Rules window. The DRC can be run at any stage of your PCB layout process. But at the end of PCB layout DRC must be run to verify there are no errors and no warnings. The DRC generates errors if any rules are violated in the PCB design against the constraints set in Design Rules Window. Other checks like LVS (Layout-Vs-Schematic) and ERC (Electrical Rule Check) can be run to ensure error free PCB.
Step-6: PCB Fabrication:
Step-6a: Photo Film:
After the PCB layout is completed, the Gerber, Drill Files and other fabrication output files are sent to CEM via email or uploaded on online portal to start working on PCB fabrication. The first step at the PCB fabrication end is the creation of Photo Film with the help of photo plotter. The photo film is actually the transparent thin sheet of plastic that can be negative or positive. The separate film is created for each layer of multilayer PCB and separate film for solder mask. The photo film is actually telling which part is the copper area on PCB and which is not copper.
Step-6b: Copper Laminate and Photo-resist:
The next step is to use the copper clad laminate substrate. i.e. FR-4 that has thin layer of copper foil pre-impregnated on both sides of FR-4 substrate with epoxy resin. The photo resist film is then applied on the copper clad laminate and then photo film is placed upon the resist. This sandwich (FR-4/Copper laminate + Photo Resist + Photo Film) is then exposed to UV radiation to develop the image of circuit on copper clad laminate. The area under the black ink will not be exposed and hence will become copper trace, while area exposed to UV will become hard and photo-resist is removed from that area.
Now the layers with excessive/unwanted copper are treated with chemical solution to etch away unwanted copper. The copper underneath the tin is protected and will make traces.
Step-6d: Layer Alignment:
For the case of multilayer PCB, with multiple internal layers, the above process is repeated for top, bottom and all inner signal layers as well. After that, all layers are aligned together very precisely on registration holes with pins. This step is crucial because if alignment is faulty then in later stages when layers are bonded/fused then we would not be able to separate each layer.
Step-6e: Layer Bonding:
In this step all the layers that are aligned are now fused together or bonded together. This is done by inserting the layer of pre-preg or adhesive between two every layers so that when layers are pressed by bonding machine under high temperature and pressure, the adhesive will melt and form a strong bond.
Step-6f: Drill Holes:
Now that we have a stack of layers, it is time to drill holes in the stack. An automated machine that uses NC Drill file, will use X-Ray system to precisely locate hole location and use high speed drill (150,000 RPM) to bore holes by moving quickly all over the PCB surface.
Now our stack has holes bored, it is time for plating the “through holes” also called PTH by means of electro-less/chemical and electrolytic plating. The walls of holes are completely/uniformly plated with copper now. A copper layer of 1 micron is deposited on walls of PTH holes by chemical plating process.
Step-6h: Apply Solder Mask:
The epoxy solder mask ink is now applied to the board surface. The areas where the solder mask is not intended (i.e. copper tracks, pads, vias) are covered while the areas uncovered will go through UV radiation which will apply solder mask to the uncovered region (region where copper is not present or where soldering is not required) while the solder mask from covered area will be removed off.
Step-6i: Surface Finish:
The surface final touch finish is either HASL, ENIG or OSP. This can be of silver or gold.
Apply silkscreen to show component designator, board details, logo with white color ink commonly used.
The last step of fabrication is v-scoring, v-groove cutting or removing individual PCBs out from the larger PCB panel.
Step-7: Prototype PCB Assembly:
The biggest next step in PCB prototype development is now to assemble components (SMT and THT) PCB top and bottom surfaces.
Step-7a: Component Sourcing:
At Rayming PCB, we have a strong relationship with cost effective components suppliers and with high quality components we can make a high quality PCBA to ease your work so you can focus on design. Your provided BOM will be our guide to purchase/source/procure components from our reliable sources.
Step-7b: Solder Paste Stenciling:
A stainless steel stencil with proper apertures are used to apply solder paste evenly at all pads on PCB surface. The solder paste will mix with flux to melt and bond with PCB surface on pad. The paste is spread on the surface and applied on every pad opening on stencil through applicator or squeegee and then the stencil is removed.
Step-7c: Component Pick and Place:
The automated robot is used to automatically pick components from reel and place them on PCB location precisely according to pick and place file that has numeric coordinates X,Y for each component
Step-7d: Reflow Soldering:
Now that the components are placed and stick to the board with glue, the board will go through the reflow oven where the board will be baked slowly up to the temperature of 480F thus melting the solder paste and creating a strong solder joint between components and pads of PCB. The reflow soldering is done only on SMT components while some remaining THT components can be soldered by hand by technicians.
Step-7e: Wave Soldering:
Wave soldering is the alternate step for reflow where THT components are soldered by automated machines splashing the molten solder on the surface of PCB on THT components legs. This process is suitable for THT components and not for SMT.
The PCB finally stuffed with SMT and THT components is now thoroughly checked for quality by performing AOI (Automated Optical Inspection) and AXI (Automated X-Ray Inspection). AOI and AXI can be done any time any stage in the bare PCB fabrication or PCB assembly process. But it is necessary to be done at final stage of quality checks. These checks include shorts, open, solder bridges, missing or misaligned components etc
Step-7g: Functional Test:
Flying probe test, bed of nails test and other various test programs can be run to check the functionality of PCB as a whole.
Step-8: Shipment and Delivery:
At this stage the PCB is ready to be shipped and delivered to the customer through logistics cell of CEM by air or sea freight.