How are Custom Functional Testers Designed?
Welcome to the first, in a series of newsletter articles on the Design of Custom Production Functional Testers. This one describes an overall view of how an organization might go about developing a tester. More will follow that take deep dives into the Tester Development process.
Often in an organization, the design engineer is called upon to design the Final Production tester for a project. This is sometimes done concurrent with, or after the product design is complete. If the company has enough experience in the product line the tendency is to just adapt, or tack something on to an existing tester.
If the product is either a brand new one, or a large change to a current one, then the company must embark on the design of a new functional tester. This can take away from the resources designing the new product. At this point, an organization might decide to bring in persons, other than the Product Design Engineers to create this tester. They might also consider bringing in outside resources to perform this task.
Approaching the Design of a New Tester
In many ways the process of designing a brand new tester is the same as designing a new product. There is a need for a:
1. Tester Development Specification
This would be the phase of the development sets that entire basis for how the tester project will proceed, and will essentially result in the tester functional specification. A design might not spend considerable time on any of the areas listed below, but most are worth consideration before proceeding with the specification. Like many specifications, the content of the Specification will evolve over time as the product design progresses.
a) Develop a Testing Strategy and Write Test Specification
- Examine the general electrical tester performance requirements
- Examine what BIST and other test related software and hardware will be designed into the unit to be tested. This is formally known as design for testability (DFT).
- Examine what pre-tests will be done on the units such as physical inspection and flying probe testing.
- Examine the economics of the tester for deployment now, at lower volumes, and in the future with higher test volumes. This can include development cost for the tester, and the cost of test resources needed to perform the testing at the earlier volumes, and the lower cost later.
- Consider the number of tester units to be built from 1 or 2 to perhaps hundreds vi. Examine the desired quality requirements for yield at production and in the field. How critical product quality to the success of the organization.
b) Write Test Specification
2. Tester Development Plan Once the specification is completed, a block diagram architecture can be made to establish the design of the hardware portion. Then a functional Firmware specification can be generated to map out the amount and type of firmware to be created for the tester. From here, an overall project plan can be created to establish the general resources during each portion of the required design to complete the tester.
The Print Circuit Board Assembly Process
Altest has always focused on providing a solution in-house to any PCBA challenges that our clients may face. Clients in the past have tasked Altest with fully taking their project from a prototype to a market-ready product through a
PCBA is short for Printed Circuit Board Assembly which is the process of combining electronic components and accessories onto blank printed circuit boards (PCB). To create electronic devices the PCB must be fabricated and then components must be added. PCBs have conductive pathways engraved onto the boards which deliver electricity to the components to operate. Assembling these boards can present unique challenges due to the varying complexities of design and the size of the boards. Different products have vastly different sizes and the capabilities of an assembly firm are dependent on what machines they have and how they set up their assembly lines. Depending on the assembling company they may not be able to manufacture large boards exceeding certain dimensions and thickness due to the machines they have. This article will touch upon the basics of the assembly process from the equipment and tools we use to the types of techniques we use.
It all begins with a design for the board itself. Clients usually have a team of in house engineers that design the boards, but if a design is too difficult or they lack an experienced engineering team they can utilize the engineers at the assembly company. Altest has a dedicated team of engineers that are able to assist during this stage of the process. Depending on the assembly company clients can order a fabricated board through them as well.
The assembly process begins with a design for manufacturing check (DFM) which validates a board design based on the manufacturer’s guidelines. A DFM check reviews a client’s designs, part spacing, pin indications, footprint corroboration, and a BOM verification just to name a few techniques Altest uses. This ensures initial errors will be caught early which will prevent delays and RMAs. Altest offers a free DFM check to ensure that a client’s project is complete on time.
A BOM check is done to provide the client with an accurate cost of materials for their project. Once we determine the validity of the BOM the next step is component procurement. Altest has a dedicated parts warehouse where components will be pulled before using third party components. Parts we order for the project are subject to our incoming material inspection check. This ensures that new parts added to our warehouse and to the project kit meet our standards and to ensure any problems will be caught before being assembled. Due to scarcity for certain parts, this may lead to longer lead times and may delay the project. In that scenario, our component engineer will assist in finding a possible alternative component that will work just as fine and speed up lead times.
There are multiple ways to assemble a PCB board. Depending on the design a board can utilize multiple techniques. Different techniques serve different purposes and can significantly impact the cost to manufacture a board. The most used form of manufacturing today, however, is a technique known as surface mounting (SMT).
Surface Mount Technology (SMT): Components are assembled by a technique called soldering. Metal pins on the components allow for easy connection to the PCB board. This technique is the most commonly used form of assembly due to speed, cost, and flexibility. Components can be assembled with higher densities and rapidly with machines. The SMT process allows for components to be mounted on both sides of the board which allows for much more complex designs on the client’s end. SMT machines can place components in the tens of thousands every hour onto PCBs.
Through-Hole Mounting (THM): This method involves drilling a hole into the PCB to attach components. Some components and electrical accessories can only be attached using this method such as input connectors. This method adds extra cost and manufacturing time to the project. Through-hole mounting is rarely used if a component can be assembled through the SMT method due to THM taking up more space and limiting design complexity while increasing cost and time to manufacture. However, if a project requires constant insertions or environmental stress then THM would be a good method to ensure longevity.
Electro-mechanical assembly: This method also known as a box-build assembly is the process of using things like custom metalwork, cable assembly, plastics, and harnesses to assemble printed circuit boards with electronic components. Some firms will elect to ship straight to the consumer when the product is made in the manufacturing facility to save on time. Altest offers this as well as RMA support staff as well as warehousing.
First, a stencil is made that allows for only the pads of the board to be in contact with the solder paste. The screen printer that applies an even coat of the paste onto the board to allow for components to be attached. Altest uses multiple high-speed EKRA and GKG screen printers that allow for large board sizes with high reliability.
Once the board has the solder paste applied to it, it then moves on to a 3D solder paste inspection (SPI) machine. This machine ensures that the correct specified thickness and amount of solder paste was added to the correct areas of the board as per the engineer’s design. This saves time down the assembly process line.
Once the solder paste on the board has been inspected we move onto machine placement of the components otherwise known as pick and place. Just like our screen printing process, Altest has multiple pick and place machines by MyData and ASM that allow us to efficiently manufacture high and low volume projects of varying sizes and complexities without impacting other projects. These pick and place machines vary in speed and capabilities so we made sure to utilize multiple machines to ensure flexibility.
Components are placed onto the board as much as tens of thousands of components an hour. This entire process is completely automated which ensures human error isn’t a factor. These machines are highly precise in their movements down to the millimeter.
Once the boards have all the necessary components placed the next step would be the reflow oven. The reflow oven applies intense heat to the board which creates a permanent solder joint between the board and component. Some components can’t withstand the heat that the reflow oven puts out so they must be hand soldered.
Some parts require wave soldering to be down. We use a machine here at Altest called a selective soldering machine as well as traditional wave soldering machines. Altest has an in house nitrogen facility that produces the necessary chemicals for wave soldering. This process is used to ensure that heat-sensitive components are not damaged or for through-hole components to be assembled.
Once this step is completed the board will go through a wash containing ionized water which will clean flux residues off. This ensures the board will perform reliably and have longevity. During this process, the board will also undergo a quick manual inspection before moving onto the next step.
A 3D AOI or automated optical inspection allows us to inspect a PCB after the reflow process. This machine can inspect double-sided boards to ensure we catch any defects that may have been missed throughout the entire process.
Our next inspection machine is an X-Ray machine that can perform non-destructive inspections on optically hidden features of the board such as joint quality confirmation and analysis; component shorts, voiding, opens and more; and other possible issues undetectable by all other inspection processes.
There are multiple forms of testing done to ensure that a PCB functions perfectly. Flying probe testers also referred to as fixture-less in-circuit tests (FICT) are the ideal testing machines for a majority of projects. The board design is uploaded to the machine and the multi probes will “fly” around and test the components on the board. These machines are extremely flexible and allow for the testing of large boards as well as double-sided designs fairly quickly.
There are also functional tests that involve monitoring and debugging the board manually after assembly. Clients may provide our team with testing programs and software that can be tested by our staff before being shipped out.
Once the board has come off the testing process line it is then taken to a final hand inspection. Once our final QC expert gives the green light on the board and ensures that each quality check stamp has been applied for each stage of assembly it is then sent to shipping. Our shipping team then cleans up each board to be sent out to the customer. Each board is carefully cleaned and inspected to ensure the optimal final product for our customer. Our shipping team then packages each board carefully following ESD (electric static discharge) guidelines and shipping safety packaging to ensure nothing damages the boards in transit. Once our customers have received the boards we still stay in close contact to ensure that there are no problems after shipping and if there are any changes that need to be in following iterations.
What is the Electro-Mechanical / Box Build Assembly Process?
Altest has always focused on providing a solution in-house to any PCBA challenges that our clients may face. Clients in the past have tasked Altest with fully taking their project from a prototype to a market-ready product through a process known as a box-build assembly. A box-build assembly is taking the initial finished PCB after it has been assembled and manufacturing an enclosure with things such as testing, packaging, software installation, etc done by the manufacturer. This eliminates the complexity of warehousing, shipping, and other complications with creating a final product for start-ups or smaller companies without an established infrastructure. Each step involved in a box-build assembly process increases in complexity depending on how fleshed out the client wants their final product to be. It is beneficial for the client and the manufacturer if there are included CAD models and packaging design already designed to expedite the manufacturing process.
The first step in the manufacturing process for a box-build project is assembling the PCB with the client’s design that accounts for the design of the final enclosure. You can find a more detailed explanation about the PCB assembly process and each step in manufacturing here. It begins with submitting a GERBER file of the PCB board as well as a BOM otherwise known as a bill of materials which will be used to quote a client’s project. Once a BOM has been approved and a price for the build is approved and submitted the manufacturer begins the process of procurement. It’s common for clients to provide some parts they may have already had on hand as well as blank PCBs as consignment parts. Altest offers the ability to procure components from our 100,000+ line item warehouse as well as our PCB fabrication partners to expedite the procurement stage of manufacturing.
Once the parts are all acquired the manufacturer can start kitting the build for the production floor to ensure that every component is accounted for. This ensures that no component is lost during manufacturing to ensure that there will be no delays due to a missing component. The blank boards go through the process of component assembly including SMT process assembly and through-hole assembly. Most box-builds require the installation of connectors such as display ports and USB ports which uses the through-hole mounted assembly process (learn more here).
Once the PCB has all the components on the board then it’s time for an optional, but recommended comprehensive test to ensure that all the board functions. This is to ensure that all the components function and there are no shorts on the board. A flying probe machine tests a board by rapidly probing each component to ensure that there are no faulty parts. After machine testing the boards there is a hand inspection to fully ensure that each board meets our QC standard as well as exceeding the client’s standard.
Once the PCB is completed and tested for any flaws then the board can be moved onto the next step which is software installation. A client should provide the necessary tools to install the board’s software which our engineering teams can learn and continue to apply to each board. This eliminates the need for the finished board to bounce between customers and manufacturers. A software installation guide is recommended with troubleshooting to ensure that there are no delays during this step to ensure rapid delivery and customer standards.
A client creates what they want as a final product which includes the PCB GERBER file, Bill-of-Materials, and enclosure CAD drawings. CAD drawings should specify the exact product measurements of the enclosure. Once a CAD drawing is finalized and materials selected we work with our plastic and metal manufacturing partners to create an affordable enclosure that meets the needs of the clients.
CAD drawings should have detailed information on the product enclosure such as dimensions, sizes, relations, aspects, properties, and characteristics of the enclosure to ensure an accurate final product. Some companies struggle with this stage, but Altest offers a highly skilled team of engineers to assist in the CAD drawing creation should the need arise.
The CAD drawings provided by the client will then be sent over to our manufacturing teams to start enclosure production to finish concurrently with the PCB boards. Our manufacturing teams are well versed in plastic and metal enclosure manufacturing with multiple finishing options such as powder coating or anodized. Once the enclosures are finished being manufactured they’ll have any labels or custom graphics applied onto them such as warranty stickers or logos. Once the boards are completed and the enclosures are ready then the boards must go through PCBA integration.
Cables and harnesses must be planned out with wire diagrams from the client to ensure easy access for servicing, testing, and compliance. Altest offers a dedicated cable/harness engineering team and is able to manufacture custom harnesses as well as expertly assemble them.
A harness is a group of wires and/or cables encased in a non-conductive durable sheath. Materials used for these coverings are typically rubber or vinyl due to their non-conductive properties. Gold, Copper, Aluminum, or many different metal alloys are used to make wires. Depending on the desired conductivity properties appropriate wire is selected.
There are mainly 2 types of wires: Solid (single conductor) and Stranded (Multiple conductors).
Solid conductor wire is constructed of one single core of the wire, whereas stranded wire is multiple strands of wire grouped together to make up the single core. Solid wires are more rigid and more durable which are commonly used in building wiring. Stranded wires are more flexible and more commonly used in robotic applications. Other cable varieties include coaxial, ribbon, shielded, twisted pair, and fiber optic cables. The AWG (American Wire Gauge) standard is used to identify the width of the wire, from very thin (0.003 inches) to 3 or more inches in thickness.
Another key factor is the airflow of the enclosure which is a key factor when a pneumatic assembly process to avoid any kinks or bends.
Pneumatic systems make use of pressured gas to actuate a device to function. They are generally powered by pressurized air or inert gases. A small or large-scale compressor is needed to power up cylinders, motors, and other pneumatic devices. Pneumatic systems are commonly used in medical, packaging, material handling, entertainment, and robotic applications. These systems are sometimes preferred because they are inexpensive, versatile, reliable, and less dangerous than electronic actuators, electric motors, and solenoids.
They can be especially helpful in hazardous conditions such as in mining operations as a stray spark could cause a reaction in certain environments. Pneumatic systems can be used in combination with various other electrical/electronic integrated systems to activate certain parts of a device. They are particularly useful where minute loads are desired.
Pneumatic systems are commonly seen in everyday items such as air brakes, nail guns, air hammers, and vacuum pumps. Sophisticated electronics are used to accurately control airflow in many robotic applications.
During the manufacturing, stage labels are added to the enclosure and boards beforehand to allow for our tracking system to manage each board in case of failure or loss which is standard for Altest regardless of a box-build. Each board can easily be tracked for RMA in case of failure and a warranty can be given to the final end-user determined by the client.
Altest has experience in packaging engineering as well as shipping logistics. We can also use any specified shipping procedures determined by the client as well such as custom packaging, labeling, and materials for purposes such as marketing. Altest has established shipping partnerships and can handle shipping logistics for the client to ensure that it reaches the end-user quickly and affordably.
Altest has a full-sized component warehouse with space to store and warehouse any box-build assembly product. Our warehouse has built-in climate control, humidity monitors, traceability software and full security to ensure the safety of a client’s product.