How to Choose Professional PCB Prototype Assembler

Written by Rush PCB Inc on . Posted in PCB, PCB Assembly and component

Source: ourpcbte.com

image: ourpcbte

 

OEMs, especially those requiring only a few boards to be assembled, may want to outsource their Printed circuit boards to a professional PCB prototype assembler, rather than assemble the boards in-house. Instead of investing in expensive production equipment, they would prefer to obtain their product from a PCB prototype manufacturer, and have an expert assemble it, so that they have reliable PCBs. Fortunately, an eminent enterprise, RushPCB, provides expert solutions for both manufacturing and assembling PCBs.

OEMs are experts in the products they manufacture, but may not be so knowledgeable about the PCBs and assemblies that make up their product. Therefore, some guidelines are necessary to enable them select the professional PCB prototype assembler most suited to their requirements.

Technical Expertise

It is very important to ensure the assembler has the necessary processes in place. For instance, if the OEM requires BGAs on their PCB, they must ensure the assembler is capable of BGA assembly and rework, and they have X-ray machines for verifying their assembly. As most PCBs use surface mount devices, the assembler should be familiar with them to the extent of using automated machinery for SMT assembly.

Depending on the quantity of boards outsourced, the assembler should preferably have automated pick and place machines, capable of handling the type of SMDs required by the OEM. Furthermore, they must also have the ability to program the pick and place machines from the data files the OEM sends them, the resources to generate stencils for solder paste and glue, multi-zone reflow soldering machine, and testing services for the boards.

Working Closely

If the OEM is outsourcing for prototype manufacturing and assembly, it is important that the assembler be willing to work with them for fixing errors in the layout, mistakes in the BOM, and parts that do not match the footprints on the board. The OEM should be able to make the most of the existing board while resolving the problems with the assembler.

The ability of the assembler to undertake turnkey projects irrespective of the volume of the job is a great advantage to the OEM. Most likely, the assembler can club together requirements of all their customers when procuring parts and in turn pass on the price advantages of bulk purchasing to their individual customers.

Also Read;   PCB Testing: Why is it Important?

Objective of the Outsourcing

To be effective, OEMs must also set their objectives that they expect from the outsourcing exercise. This is important, as the objectives may vary. For instance, some may be planning to outsource a single product, others may be shifting their growing volumes to a partner with a higher production capacity, while still others may be looking for reducing costs.

Pre-Qualifying Questionnaire

While selecting a suitable PCB prototype assembler, it is a usual practice to send them a pre-qualifying questionnaire. This must be short and address the most vital points. While including an overview of the OEM’s company and information on the product type to be assembled, the main idea in sending out the questionnaire would be to determine in advance if the assembler is a potential fit.

Request for Quotation

When the OEM sends an RFQ or request for quotation to a PCB prototype assembler, it is important they provide all the commercial and technical information the assembler would need. This holds true even when the OEM is looking for a potential PCB prototype manufacturer. For instance, it should contain information such as lead-time, functional testing requirements, component substitution required, estimated annual usage, quantity per production, turnkey requirement or consigned assembly, and any other requirement.

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Management Aspects

To ensure smooth working with the prototype assembler, it will be advantageous to the OEM if they periodically audit their partner, making sure the team has as wide a range of skills as possible. If necessary, the OEM can transfer some of their skills and knowledge to their partner. A good management practice is to establish regular meetings to make sure activities move on schedule, and the relationship can be discussed at higher levels, while the OEM outlines their strategic plans for the future.

Conclusion

Rush PCB, being both, a professional PCB prototype manufacturer as well as a PCB prototype assembler, can handle not only prototype jobs, but also take up regular production works and turnkey projects. It meets all the above criteria, has the necessary quality management systems in place, and has the necessary technology and expertise to handle the most complicated board assemblies.

 

Key Elements of an Ideal PWB Material from Rush PCB Inc.

Written by Rush PCB Inc on . Posted in PCB, PCB Assembly and component, PCB Manufacturing

Printed Wiring Materials (PWBs) from Rush PCB Inc. are available in huge diversity and wide range of applications. This has made the concept of any ideal laminate very fuzzy, to say the least. For instance, a material suitable for a high temperature application may be impractical for high-speed digital design such as in a microwave. Therefore, although it is possible to list potentially important properties, each design team will need to establish a prioritization among them since no one material will present the optimal value for all properties that might be considered to be important. Essentially, Rush PCB Inc. presents some common ingredients or properties of PWB materials listed below, from which designers can make their choices during the design phase.

Tg—Glass Transition Temperature

Polyimides with Tg of 250°C or above are suitable for the highest temperature systems. Designers consider Tg as a rough indicator for total Z-axis expansion and hence, a proxy for reliability indication for plated through holes. For applications where either in-use temperature or process temperatures (or both) are less demanding, manufacturers offer a wide variety of epoxy systems with Tg in the range of 170°C.

Tg offers a good frame of reference for polyimide and traditional epoxy materials. However, it is not reliable for characterizing the reliability of non-traditional resin systems and highly filled systems used in high frequency and low loss applications where the PWB is a composite of various components.

Td—Thermal Decomposition Temperature

Depending on the chemical composition of PWB materials, this property may vary greatly form the mid 300°C range for several epoxy systems to over 400°C for some polyimides. When a PWB material reaches its Td temperature, it begins to degrade thermally. In general, data sheets list Td temperature as one at which the material loses 5% of the original weight due to decomposition.

However, the onset temperature at which significant weight loss of PWB material begins to occur, presents a better indicator of performance. The reason being by the time the material has lost 5% of its weight from decomposition, it might be totally unsuitable for any application.

Loss Tangent and Dielectric Constant

A signal passing along a transmission line on a dielectric material loses its power. Loss tangent is a measure of how much power the signal has lost. Dielectric constant is a measure of the speed of an electric signal as it travels in a dielectric material, relative to the speed of light in vacuum—the dielectric constant of space (vacuum) being defined as 1.00. Therefore, a higher dielectric constant for the PWB material implies a slower propagation speed through it.

Dimensional Stability

Etching causes shrinking in all laminate materials to some degree, while consistency of both process and product depends on the consistency in registration. A suitable PWB material would be one that shrinks minimally when etched, has consistent and reproducible shrinkage that allows predictable factors for artwork compensation. Ideally, the PWB material should not require any artwork compensation, and should always register properly, without requiring any compensation while drilling. The IPC test of dimensional stability is at best a measure of the actual registration of a specific board design, and registration continues to be a major fabrication concern for HDI and high layer count designs.

CTE—Coefficient of Thermal Expansion

Designers must match the expansion requirements of PWB materials to the expansion requirements of devices to be mounted on the surface, claddings, and the thermal planes buried in the interior. For instance, a CTE of 6 ppm/°C is ideal for leadless ceramic chip carrier attachments, and laminates such as Arlon’s 45NK woven and reinforced with Kevlar with low resin contents are suitable. Rush PCB Inc. tend to use other material also, such as nonwoven aramid reinforcements, copper-invar-copper distributed constraining planes, and quartz reinforcements for achieving values as low as 9-11 ppm/°C. This represents a substantial improvement over conventional polyimide or epoxy laminates and such PWB materials have proven consistent and acceptable in a variety of SMT designs.

Also Read;    Manufacturing Process of Printed Circuit Boards

Tc—Thermal Conductivity

With increasing density of components on a board, required for meeting the demands of improved functionality, as against a steady decrease of the overall surface area of PWBs, the watt-density of power the PWB generates also increases. As critical devices could fail at rates doubling for every 10°C increase of temperature, this pushes designers to use PWB materials with high thermal conductivity to remove heat directly from devices placed on the surface of the board.

However, designers must do this without allowing the board to suffer in terms of dielectric and electrical properties. While traditional polyimide or epoxy systems have thermal conductivity values between 0.25 and 0.3 W/m-K, Rush PCB Inc. targets thermal conductivity figures in the 1.0 to 3.0 W/m-K range, to achieve significant reduction in the board surface temperatures, especially near active devices.

Expansion in the Z-Direction

For the ideal PWB material, expansion in the Z-direction must match that of copper within the PTH to avoid damaging the plating inside the holes during thermal excursions in processes such as solder reflow. Typically, standard materials exhibit CTEs of 50-60 ppm/°C, when the operating temperature is below Tg, while this increases to roughly four times higher when the temperature crosses Tg. PWB materials with high Tg value, such as Polyimides, show a lower overall Z-direction expansion than typical epoxy systems do.

Compatibility with Lead-Free Processes

PWB materials compatible with lead-free processes need to withstand higher soldering and reflow temperatures associated with lead-free solder systems—typically 30 to 50°C higher than traditional lead-tin systems. Manufacturers usually characterize PWB material suitable for lead-free systems in terms of Tg>155°C, Td>330°C (for 5% decomposition), and overall CTE<3.5%.

This classification includes materials such as Polyimides as being lead-free compliant, while Rush PCB Inc. is using newer generations of epoxy systems to meet additional requirements. Lead-free systems are inherently more complex, as several current laminate materials can survive its applications, but some devices mounted on the boards may not even have been tested at the highest lead-free temperatures. Therefore, the trend is to use materials that have a margin of safety in the range of higher temperatures as seen during lead-free soldering.

               

Also Read;   PCB Testing: Why is it Important?

 

Green Prepreg and Laminate

Green PWB materials are typically compliant to UL-94 V0 flammability ratings specifically achieved without the use of brominated flame-retardants. Although most manufacturers use the brominated bisphenol-A for FR-4 systems, there is a movement towards non-brominated systems wherever possible, as these are more environmentally friendly.

Meeting Environmental Regulations

Several countries are now complying with regulations such as those modeled on RoHS and WEEE from the European Union, or are in the process of developing their own. The cost of compliance to multiple independent and different regulations becomes a significant part of the cost of a finished PWB.

Simple Processing

Ideally, manufacturers should be able to process the laminate and prepreg in simple ways using regular methods of photo-imaging, etching, processing through wet chemicals, and traditional techniques of lamination. High process yields and design flexibility demands the ideal material be used in multiple designs with high probability of success. Although most manufacturers still define normal processing as being suitable for the conventional FR-4 material, Rush PCB Inc. uses advanced materials in high performance PWBs that require more than the normal ideal processing.

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Problems with the Gerber File Format and Solutions

Written by Rush PCB Inc on . Posted in PCB Assembly and component, PCB Design, PCB Manufacturing, Uncategorized

The world over, a majority of designers and fabricators follow the Gerber RS-274X as the de facto standard when designing and fabricating their PCBs. The evidence of its popularity notwithstanding, Gerber has a number of practical limitations. Often, these limitations lead to a variety of problems when fabricating PCBs.

Brief History of the Gerber File Format

Ucamco developed the Gerber file format in the 1960s, when it was the Gerber Systems Corporation, and a leading provider of early photo-plotter systems using numerical controls. Their first format, RS-274D, was a subset of EIA RS-274-D, supporting their vector-based photo-plotters. Widely adopted, RS-247D remained the standard format for vector-based photo-plotters until the 1980s.

Raster scan plotters began replacing vector-based photo-plotters in the 1980s. These newer plotters were bitmap-based, requiring a completely different data format. Consequently, in 1998, Barco ETS, who had acquired Gerber Systems, released a single standard image format, and named it the Extended Gerber or GerberX. This was later renamed as the RS-274X format and is still in use today.

The latest Gerber RS-274X presents a complete image description format. Therefore, the Extended Gerber file holds the complete description of a layer of the PCB, and provides the operator with everything necessary to generate a PCB image, including the definition of any aperture shape. Requiring no external aperture files, painting, or vector-fill, the RS-274X standard specifies all pads and planes clearly and simply. Its simplicity has made it the de facto standard followed by nearly 90% of the world’s PCB designers and fabricators.

Problems with the Gerber File Format

Despite its wide acceptance and use, the RS-274X Gerber file format has its own shortcomings. The trouble is the standard does not address all aspects of fabrication and assembly, as required by the PCB fabricator.

Although Gerber RS-274X is extremely accurate and reliable when rendering images of copper shapes precisely on signal and plane layers, it does not transfer the layer stackup order accurately. Moreover, data sets and information regarding materials, drill data, netlist, pick-and-place data, bill of materials, test point reports, and more need to be generated by separate processes by different utilities. This means, the Gerber RS-274X format is incapable of transferring the complete information from the design domain to the manufacturing domain.

In the absence of a defined layer order being transferred to the manufacturer, fabrication has no way of deciding the order of copper layers and may miss a layer or two altogether. With the layer order missing, the drill data may generate holes relative to an incorrect layout. This mismatch can happen with the entire assembly data, and at all aspects of the fabrication process. Usually, with Gerber RS-274X, there is no defined way a fabricator can know about missing output data, wrong source file version, and these can render boards useless.

Designers usually get over the above shortcomings using a well-maintained design methodology and best practices shared with the fabricators. In general, they utilize Gerber RS-274X with minimum fabrication issues. However, maintaining ideal conditions all the time is difficult, things can slip up, causing problems to the fabricator and assembly houses, and now they have to face the brunt of the responsibility and sort through the issue. This also leads to fabricators and assembly houses being forced to spend a great deal of time and resource in inspecting and verifying the entire data for all incoming jobs, simply to minimize manufacturing issues.

Solutions and Alternatives to the Gerber File Format

Eminent PCB manufacturers such as Rush PCB Inc., eliminate the problems by adopting design transfer standards that addresses all aspects of the fabrication and assembly process. Two new open standards are available, and these enable efficient and accurate data exchange from the PCB designer to the manufacturing fabricators and assemblers. Ucamco administers one of these standards, the Gerber X2, while the IPC Consortium administers the other, the IPC-2581. Both are open standards, free from any proprietary restrictions.

The Gerber X2 File Format

The Gerber X2 is an expanded version of the GerberX format. In addition to the layout image data, Gerber X2 now includes design data as well. The X2 fabrication files now include the board layer order and stackup information that so far, fabricators had to interpret and verify manually. In the same way, a set of drill files is also included within the X2 fabrication files, detailing the location, drill size, plated/non-plated information, and the layer span.

The X2 attribute system qualifies objects with specifications such as file function, part, pad function, and more that add intelligence to the traditional image data improving the automation process. For instance, the file function specifies a file as top copper layer, top solder mask, while part specifies whether the PCB is a single or a panelized array, and pad function defines the pad as belonging to a via, through-hole, SMT, or fiducial. The Gerber X2 format directs all outputs to one single folder.

As the Gerber X2 is both forward and backward compatible with the RS-274X standard, it helps any X2 reader to interpret Gerber RS-274X files correctly. Therefore, fabricators using the Gerber X2 process will have no trouble interpreting legacy fabrication files created in the Gerber RS-274X format and vice versa.

The IPC-2581 File Format

Contributors from a wide range of PCB industry segment initiated, developed, and drove the IPC-2581 standard. These industries included MES, CAD/CAM and PLM vendors, PCB fabricators, contract manufacturers, as well as OEMs.  The IPC-2581 is a single data format and within a single file, contains all aspects of the PCB design, such as layer stackup, materials, assembly, and test details.

With the IPC-2581 standard, the designer can include details of layer stack and information on materials to ensure proper layer order. The standard is suitable for stackups of complex board design such as related to rigid-flex boards, and is capable of handling special materials. It can also include drill and mill data for blind, buried, and filled via types. It also supports information on back drilling, V-grooves, slots, and cavities. For bare board testing, designers can include the net-list as well.

In addition to a complete set of fabrication data, the IPC-2581 can also hold assembly data. Therefore, it can contain not only the pick-and-place information, but also the information on polarity and rotation of a component, enabling support for both stacked and embedded components.

In addition to assembly drawings, the IPC-2581 standard has the capability to generate the documentation for bill of materials and purchasing. Therefore, the standard can tie up with PLM/ERP system data to create links between design and supply chain facilities. The greatest advantage of the IPC-2581 is one single file containing the entire data related to fabrication and assembly.