PCB Prototype the Easy Way

Full feature custom PCB prototype service.

Printed Circuit Board (PCB) Assembly Services Process

PCBWay has prototype PCB,PCB Production fabrication and pcb assembly capabilities.

Surface Mount Assembly Process

Originally, all PCBs were assembled by hand using only a solder iron. As technology progresses, components get smaller and more difficult to assemble by hand and the amount of components that may fit on a single board increases. Thus the need for auto assembly was developed.

2 layers board Mixed Assembly

Required Elements

The following are the required elements for auto assembly:

  • Gerbers in 274-X (embedded apertures) including fabrication drawing.

  • Part centroid text file with Reference Designators, external placement layer, and X & Y location and rotation in ASCII format.

  • Numerical control (NC) drill files

  • Solder paste file (one of the Gerber files) for all sides mounted

  • Glue dot file

  • If possible, the design database, specifying the database format (program name)

  • Parts list or BOM (bill of material)

  • Parts or hardware required

The Gerber files are used to define the pad locations and help the assembly house determine where pin 1 is located and provides a heads-up of how the board looks. The database can also be used to determine the location of pin 1. Some board houses choose to make their own solder paste file/stencil. The designer may create the solder paste file to his/her own preference with experience. It is good to learn how and why the assembly house makes its stencils and duplicate it to ensure consistency from each assembly house (the common name for any company that assembles boards). The solder paste file is used to mask the entire board except those areas that will be soldered. Solder paste is applied to the exposed pads and the stencil is removed. Components are applied and held to the board by the solder paste and the glue dots securing the components as they are soldered to the board.

For component placement a part placement/centroid file is required to know where the center of the part is. The layer ID shows what side the part is placed on, and the rotation displays the orientation of the component.

Consistency in rotation of the original component is critical to report. Unless the designer's software can account for inconsistencies, all components should be created in the same orientation.

NC drill files are used to locate mounting holes and provide the holes sizes for thru-hole components. This also allows the assembly house to determine adequate clearance for the component lead.

A bill of material or parts list is used to reference the designators of the centroid file and the components that need to be mounted. The BOM should also provide information if the component is an SM component or a thru-hole component.

Other Considerations

Other considerations for auto assembly are the board size, the panel size, and breakaways. The boards are commonly assembled in a panel that may contain many boards. The panel is the original material that the boards were etched routed in. The panels pass to the assembly house with all boards intact.

Note

Breakaways are the connections around a board that hold the board during assembly but can be broken easily when it is time to remove the board.

1.Ordering a Board

PCBWay One-Stop Solution for PCB & Prototype Assembly,

2.DFM Check

The DFM check looks at all the design specifications of a PCB. Specifically, this check looks for any missing, redundant or potentially problematic features. Any of these issues may severely and negatively influence the functionality of the final project. For example, one common PCB design flaw is leaving too little spacing between PCB components. This can result in shorts and other malfunctions.
By identifying potential problems before manufacturing begins, DFM checks can cut manufacturing costs and eliminate unforeseen expenses. This is because these checks cut down on the number of scrapped boards. As part of our commitment to quality at a low cost

PCB DFM

3.Incoming Quality Control(IQC)

PCBWay Verifying all incoming materials and handling quality problems before subsequent SMT assembly begins. Our IQC position will check following issues of incoming materials if they comply with our strict requirements.

• model number and quantities according to BOM list

• shape (deformation, broken pin, oxidation etc), particularly for IC or other complex components

• sample test of incoming materials by tools such as test frame, multimeter etc.

• If above defect or discrepancy occurs, we will return full incoming materials to supplier or customer.

4.Machine programming - Gerber / CAD to Centroid / Placement / XY file

Having received the PCB panels and components the next step is to setup the various machines used with the manufacturing process. Machines such as the placement machine and AOI (Automated Optical Inspection) will require a program to be created which is best generated from CAD data but quite often this isn't available. Gerber data is almost always available as this is the data required for the bare PCB to be manufactured.

5.Solder Paste Printing

The first machine to setup in the manufacturing process is the solder paste printer which is designed to apply solder paste using a stencil and squeegees to the appropriate pads on the PCB.

Solder Paste Printing

6.Component Placement

Once the printed PCB has been confirmed to have the correct amount of solder paste applied it moves into the next part of the manufacturing process which is component placement. Each component is picked from its packaging using either a vacuum or gripper nozzle, checked by the vision system and placed in the programed location at high speed.

There is a large variety of machines available for this process and it depends greatly on the business to what type of machine is selected. For example if the business is focused around large build quantities then the placement rate will be important however if the focus is small batch/high mix then flexibility will be more important.

Component Placement

7.Pre-Reflow Automated Optical Inspection (AOI)

Following the component placement process it is important to verify that no mistakes have been made and that all parts have been correctly placed before reflow soldering. The best way of doing this is by using an AOI machine to make checks such as component presence, type/value and polarity.

AOI Check

8.Reflow Soldering

Once the components are placed on the boards, each piece is sent through our reflow machines. This means the solder paste needs to solidify, adhering components to the board. PCB assembly accomplishes this through a process called "reflow. "

This would appear to be one of the less complicated parts of the assembly processes but the correct reflow profile is key to ensure acceptable solder joints without damaging the parts or assembly due to excessive heat.

When using lead-free solder a carefully profiled assembly is even more important as the required reflow temperature can often be very close to many components maximum rated temperature.

Reflow Soldering

9.Post-Reflow Automated Optical Inspection (AOI)

The last part of the surface mount assembly process is to again check that no mistakes have been made by using an AOI machine to check solder joint quality.

Often, movement during the reflow process will result in poor connection quality or a complete lack of a connection. Shorts are also a common side effect of this movement, as misplaced components can sometimes connect portions of the circuit that should not connect.

Checking for these errors and misalignments can involve one of several different inspection methods. The most common of these inspection methods include the following:

  • Manual Checks
  • Automatic Optical Inspection(AOI)
  • Automated X-ray inspection(AXI)

aoi inspection

10.Conformal Coating

Some completed Printed Circuit Board Assemblies have a conformal coating. It's usually depends on the customer's product requirements.

11.Final Inspection and Functional Test

After the soldering and conformal coating step of the PCB assembly process is finished, a final inspection will test the PCB for its functionality by our Quality Assurance team. This inspection is known as a "functional test". The test software and tools are usually provided by the customer, PCBWay can also make fixtures according to customer requirements. The test puts the PCB through its paces, simulating the normal circumstances in which the PCB will operate. Power and simulated signals run through the PCB in this test while testers monitor the PCB's electrical characteristics.

12.Washing and Drying

Suffice it to say, the manufacturing process can be a filthy one. Soldering paste leaves behind some amount of flux, while human handling can transfer oils and dirt from fingers and clothing to the surface of the board. Once all is said and done, the results can look a little dingy, which is both an aesthetic and a practical issue.

13.Packing and Shipping

anti-static packaging

All assembled boards are packaged (can request in anti-static packaging) and shipped DHL,FedEx,UPS,EMS,and so on. Any unused components are returned in accordance with customer instructions. Additionally, customers are notified via email when their packages ships.

  • MANNI Automatic solder paste printing presses

  • Automatic printing presses DSP-1008

  • HITACHI Paste inspection machine

  • JUKI

  • JUKI Mounter

  • JUKI High-speed line

  • SMT Automatic production line

  • NS-800II Reflow

  • SMT-AOI2

  • SMT-AOI4

  • X-RAY

  • First piece tester

  • BGA Rework

  • DIP Automatic line

  • DIP Self-welding assembly line

  • Wave soldering

  • Soldering robot

  • Oscilloscope

  • Automatic aging rack

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quotesI am impressed with the quality of the boards, the delivery time and responce to all my questions. Best price excellent service and speedy delivery. When I need another board I will certainly use this supplier. "

-Bill Robinson Company

quotesспасибо за платы! платы очень хорошего качества. надежный продавец. оперативно отвечал на вопросы. заказ выполнили и отправили очень быстро.Заказываю платы не в первый раз - как всегда только лучшие впечатления. 5+++. 4 числа отправил файлы 26-го забрал на почте в Москве."

-FVL. SKU Company
Front-end data preparation

01.PPE - Pre Production Engineering

Customer supplied data (gerber) is used to produce the manufacturing data for the specific PCB (artworks for imaging processes and drill data for drilling programs). Engineers compare demands/specifications against capabilities to ensure compliance and also determine the process steps and associated checks. No changes are allowed without PCBWay Group permission.

Preparing

02.Preparing the phototools

Artwork Master is PCB production in the key steps, which directly affect the quality of the final product quality,An accurately scaled configuration of electronic data used to produce the artwork master or production master. Artwork Master – The photographic image of the PCB pattern on film used to produce the circuit board, usually on a 1:1 scale.In general, there are three types of Artwork Master:(1) Conductive Pattern  (2) solder mask (3) Silkscreen

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03.Print inner layers

Stage 1 is to transfer the image using an artwork film to the board surface, using photosensitive dry-film and UV light, which will polymerise the dry film exposed by the artwork.
This step of the process is performed in a clean room.
Imaging – The process of transferring electronic data to the photo-plotter, which in turn uses light to transfer a negative image circuitry pattern onto the panel or film.

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04.Etch inner layers

Stage 2 is to remove the unwanted copper from the panel using etching. Once this copper has been removed, the remaining dry film is then removed leaving behind the copper circuitry that matches the design.
Etching – The chemical, or chemical and electrolytic, removal of unwanted portions of conductive or resistive material.

aoi icon

05.Inner layer Automatic Optical Inspection(AOI)

Inspection of the circuitry against digital “images” to verify that the circuitry matches the design and that it is free from defects. Achieved through scanning of the board and then trained inspectors will verify any anomalies that the scanning process has highlighted. PCBWay Group allows no repair of open circuits.

Lamination icon

06.Lay-up and bond (Lamination)

The inner layers have an oxide layer applied and then “stacked” together with pre-preg providing insulation between layers and copper foil is added to the top and bottom of the stack. The lamination process consists of placing the internal layers under extreme temperature (375 degrees Fahrenheit) and pressure (275 to 400 psi) while laminating with a photosensitive dry resist. The PCB is allowed to cure at a high temperature, the pressure is slowly released and then the material is slowly cooled.

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07.Drilling the PCB

We now have to drill the holes that will subsequently create electrical connections within the multilayer PCB. This is a mechanical drilling process that must be optimised so that we can achieve registration to all of the the inner layer connections. The panels can be stacked at this process. The drilling can also be done by a laser drill

copper icon

08.Electroless copper deposition

The first step in the plating process is the chemical deposition of a very thin layer of copper on the hole walls.
PTH provides a very thin deposit of copper that covers the hole wall and the complete panel. A complex chemical process that must be strictly controlled to allow a reliable deposit of copper to be plated even onto the non-metallic hole wall. Whilst not a sufficient amount of copper on its own, we now have electrical continuity between layers and through the holes.Panel plating follows on from PTH to provide a thicker deposit of copper on top of the PTH deposit – typically 5 to 8 um. The combination is used to optimise the amount of copper that is to be plated and etched in order to achieve the track and gap demands.

image icon

09.Image the outer layers

Similar to the inner layer process (image transfer using photosensitive dry film, exposure to UV light and etching), but with one main difference – we will remove the dry film where we want to keep the copper/define circuitry – so we can plate additional copper later in the process.
This step of the process is performed in a clean room.

Plating icon

10.Plating

Second electrolytic plating stage, where the additional plating is deposited in areas without dry film (circuitry). Once the copper has been plated, tin is applied to protect the plated copper.

etch icon

11.Etch outer layer

This is normally a three step process. The first step is to remove the blue dry film. The second step is to etch away the exposed/unwanted copper whilst the tin deposit acts an etch resist protecting the copper we need. The third and final step is to chemically remove the tin deposit leaving the circuitry.

AOI

12.Outer layer AOI

Just like with inner layer AOI the imaged and etched panel is scanned to make sure that the circuitry meets design and that it is free from defects. Again no repair of open circuits are allowed under PCBWay demands.

Soldermask

13.Soldermask

Soldermask ink is applied over the whole PCB surface. Using artworks and UV light we expose certain areas to the UV and those areas not exposed are removed during the chemical development process – typically the areas which are to be used as solderable surfaces. The remaining soldermask is then fully cured making it a resilient finish.
This step of the process is performed in a clean room.

Surface finish

14.Surface finish

Various finishes are then applied to the exposed copper areas. This is to enable protection of the surface and good solderability. The various finishes can include Electroless Nickel Immersion Gold, HASL, Immersion Silver etc. Thicknesses and solderability tests are always carried out.

Profile

15.Profile

This is the process of cutting the manufac-turing panels into specific sizes and shapes based upon the customer design as defined within the gerber data. There are 3 main options available when providing the array or selling panel – scoring, routing or punching. All dimensions are measured against the customer supplied drawing to ensure the panel is dimensionally correct.

Electrical test

16.Electrical test

Used for checking the integrity of the tracks and the through hole interconnections – checking to ensure there are no open circuits or no short circuits on the finished board. There are two test methods, flying probe for smaller volumes and fixture based for volumes.We electrically test every multilayer PCB against the original board data. Using a flying probe tester we check each net to ensure that it is complete (no open circuits) and does not short to any other net.

inspection

17.Final inspection

In the last step of the process a team of sharp-eyed inspectors give each PCB a final careful check-over.Visual checking the PCB against acceptance criteria and using PCBWay “approved” inspectors. Using manual visual inspection and AVI – compares PCB to gerber and has a faster checking speed that human eyes, but still requires human verification. All orders are also subjected to a full inspection including dimensional, solderability, etc.

Packaging

18.Packaging

Boards are wrapped using materials that comply with the PCBWay Packaging demands (ESD etcetera) and then boxed prior to be being shipped using the requested mode of transport.