Tag Archives: pcb prototype assembly

Work with PNC to Reduce PC Board Costs

Work with PNC to Reduce PC Board Costs

When it comes to reducing the manufacturing cost of a PCB, it is important to remember that a significant part of the cost of a PCB assembly is already baked in at the design concept stage.  The product concept defines the PCB size and shape, while the performance of the system dictates the microprocessor, memory and other functional elements of the circuit.

However, some of the assembly cost can still be affected by design choices made by the PCB designer.  A PCB that is designed for manufacturing (DFM) can reduce both the fabrication cost of the PCB and the costs of component assembly and soldering. A DFM approach to design can also reduce the likelihood of the hidden costs of poor yield in production.

The best way to achieve the lowest cost, most manufacturable design is to work closely with the prospective  manufacturer, since the way to maximize DFM cost savings is to design for a manufacturer’s specific equipment and technology, rather than to rely on general rules.

Reducing PCB Fabrication Costs

The first step to reducing costs in PCB fabrication to reduce the number of operations performed by the manufacturer.  The second step is to optimize the PCB design to leverage a manufacturer’s particular fabrication technology.

One way to reduce costs is to eliminate or minimize the amount of machining required around the board edge or within the PCB itself.  Rectilinear PCB outlines without internal slots will minimize machining, and the rectangular shape allows the PCB to be grouped in larger panels that are separated after assembly.  These large panels streamline assembly by allowing a several PCB to go through component assembly and reflow at the same time, improving throughput. For example, PNC can process a maximum panel size of 18” X 24.” To ensure that the components on the PCB are not damaged during the scoring and separation from the panel, components should be kept 200 mil from the board edge.

Reducing board layers to reduce fabrication costs

The generally accepted rule that reducing the number of PCB layers in a stack-up will reduce cost has become more complicated with the advent of HDI technology.   The reason is that the cost of an additional Printed Circuit Board layer is not linear, so a cost calculation needs to be made for each jump in the number of layers. Is it cheaper to use finer trace widths and buried vias to reduce the layer count from six to four?  Only the manufacturer is going to know.  However, as a board gets past eight layers costs increase non-linearly with each additional layer.  The aspect ratio of the through hole vias begin to become a factor, as well as the sheer number of vias that need to be drilled and plated to connect all those layers.   At an eight layer stack up or above, the additional cost of HDI technology begins to make economic sense if it is used to reduce the number of stack-up layers required.

Respect drill to copper clearance and aspect ratio design rules

Respect the design rules for hole sizes and hole to copper clearance.  If the real estate on the PCB allows it, selecting hole sizes clearances and annular ring sizes larger than the absolute minimum will improve fabrication yield. Here are the through hole design rules for PNC:

Non-Plated Through Hole (NPTH)
● Finished hole size (minimum)= 0.006″
● Edge to edge clearance (from any other surface element) (minimum)= 0.005″
Plated Through Hole (PTH)
● Finished hole size (Minimum) = 0.004″
● Annular ring size (Minimum)= 0.004”
● Edge to edge clearance (from any other surface element) (minimum) = 0.009″

PCB assembly
PCB assembly

Reducing PCB Assembly Costs

To reduce assembly costs the objective is the same as reducing PCB fabrication costs; reduce the number of operations, and optimize the PCB design to leverage a manufacturer’s particular fabrication technology.

One easy way to reduce assembly costs is to stay away from the smallest passive packages.  0603 passives are easier to place than 0402 or the almost invisible 0201.  If possible, chose active parts that have leads rather than ball grids, because they are easier to place, they can be visually inspected instead of x-rayed, and they are easier to rework.

Avoid parts that have to be manually soldered.

Manual operations are always expensive, and the designer should do everything they can to avoid the need for them.

Component manufacturers have recognized this and now offer through-hole components (typically connectors) that can be reflow soldered.  This technology called “Through-Hole Reflow” allows through-hole components to be soldered in the same reflow process as the SMD components, eliminating a pass through the wave soldering machine or manual soldering.

Finally, if possible, avoid putting components on both sides of the board.  The cost of a higher density PCB with components on one side may be cheaper than a lower density PCB with components on both sides.

Don’t wait until the PCB design is finished before talking with PNC

The best time to talk with the PC Board design experts at PNC is early in the layout process.  They can tell you when to use HDI to reduce costs and can advise on how to optimize panel size. The experts in the assembly department can also work with you to select components that will reduce assembly costs and increase yield.

Give PNC a call today.

Embedded software development along with PCB Assembly

Embedded software development along with PCB Assembly

No company can excel at every aspect of new product development and trying to do everything can dilute an organization’s focus on the tasks that are essential to its success. For example, most companies have long ago outsourced the PCB design and fabrication steps of new product development. This same need to focus on the essential is true of software development too. It is difficult for a software company to excel at every type of software development because of the ever expanding universe of software languages, operating systems, and architectures.  A cloud based SAAS or PC based application is very different from embedded software running C on a 16-bit processor, and it takes very different software development skills to develop that kind of embedded application.

Unlike cloud based or PC based applications, embedded software is optimized to run on a specific custom hardware platform with limited processing power and memory.  It often runs on a real time operating system or no operating systems at all, and the interface of an embedded device may consist of only a small display, or just a few buttons and LEDs.

The unique challenges working with embedded systems is why many software companies outsource their embedded software projects to experts like PNC.  Here are three reasons why they do.

The embedded system is not the organization’s primary product line.

Many products on the market require options or accessories that are important to the customer, but not are not similar technically to the primary product. A cable set top box remote is a good example.  Customers expect a cable set-top box to have a remote, but the low power microcontroller embedded in the remote is likely to be completely different from the high power processor and OS driving the set-top box functions.  Similarly, Industrial or commercial equipment may have optional modules to provide additional functionality like a cellular modem.   These optional modules have independent processors and embedded software which is unrelated to the primary product software.

In these cases, software companies will choose to focus their development resources on the primary product, recognizing that it is more cost effective to outsource the software development for the ancillary embedded products to a company that is familiar with embedded microcontrollers and the constraints that come with low power operation. If that company can design the hardware and perform SMT assembly too, it becomes an even better value.

Embedded software development along with PCB Assembly
Embedded software development along with PCB Assembly

The software is deeply embedded and invisible to the user

Successful software companies are highly focused on the customer experience with their product. They are constantly refining the look and feel of the industrial design and user interface to make the product more attractive, and easier to use.  But what if the product doesn’t have a user interface?   What if it is a router or a motor controller?  Products like these need a simple interface for initial configuration, but they typically operate in the background, invisible to the customer.  In this case the goal is to optimize for cost and performance rather than user experience.  Deeply embedded applications without a sophisticated customer facing interface  are ideal to outsource to a company like PNC because the product requirements are centered on the embedded functionality – there is no need to maintain the same look and feel as the company’s customer facing products.

The application requires specialized expertise

 Sometimes a software company needs embedded expertise that it just doesn’t have in-house.  For example, they may need a Zigbee or Bluetooth RF stack, or expertise with digital signal processing on low power Digital Signal Processors DSP.  In some challenging embedded applications, a company may need a partner with the expertise to  iterate the design of both the hardware and software simultaneously to arrive at an optimized embedded solution.  In that case you need a full service provider like PNC.

PNC offers the full solution to developing embedded products

When it comes to product development, PNC is not just a PCB manufacturer.  The engineers at PNC can work with you to design and manufacture the product hardware, and then develop the embedded software to run on that hardware.   If you have a challenging embedded software or hardware project, contact PNC today and find out how they can help.

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Let PNC Simplify Your Printed Circuit Board Design With, CPLDs

New product designs continue to get more compact, while the performance and the number of features that customers expect continue to increase. To the engineer, this means higher PCB circuit densities and less room on the PCB for just-in-case design, such as unallocated I/O, or 0 ohm resistor networks to allow for reconfiguration of the PCBs at PCB assembly.

Meanwhile, new product prototype cycles are also getting faster. 3D printed mechanical parts are available within hours, putting pressure on electrical engineers to work faster and get their PCB designs right the first time. Even the fastest PCB fabrication, such as PNC’s 24-hour fabrication turn-time can’t help if the PCB has to be redesigned to fix errors.

The answer to both problems may be the CPLD. PNC’s CPLD programmers can help engineers reduce PCB size and allow on the fly circuit reconfiguration. Most people know that PNC specializes in fast PCB prototyping, but PNC is more than aPCB Manufacturer, PNC can speed prototyping by designing PCBs that replace inflexible circuit designs with PCBS that can be reconfigured to remap I/Os or change the order that circuit elements power up. A CPLD design developed by PNC can also allow the same PCB to be reconfigured to be used for the next generation product.

When it comes to programmable circuit elements, FPGA and microprocessors get all the good press. They are powerful, versatile, and generate more revenue for the manufacturers than workhorses such as CPLDS. Even though CPLD capability has improved dramatically over years, while both cost and power consumption have dropped, they are still often considered only for low level tasks such as “Glue Logic.” PNC designers can tell you that even a CPLD used for “low level” glue logic is appreciated when a late breaking design change means that two outputs now need to be two inputs, and one input needs to be inverted. All in a day’s work for PNC.

A PC Board Manufacturer, such as PNC can help you use these new, more capable CPLDs in places that can solve tough problems, replacing more expensive, complex and power-hungry solutions. Here are four examples.

I/O expansion

One of the most common CPLD applications is to expand the number of available microprocessor I/O ports. The CPLD I/O can either be multiplexed to the microprocessor or controlled via a serial interface. The advantage of a serial bus interface is that it allows you to locate this extra I/O anywhere, even on another Printed Circuit Board through a compact two or three pin connector.

The CPLD combinational logic architecture allows the creation of either a big fan-in or fan-out (over a hundred ports in some cases), and the outputs have enough current to drive small LEDS, a great way to create an array of circuit status LEDS.

When the CPLD output is used in conjunction with a CPLD’s internal clock the CPLD can also drive multiple PWM outputs allowing it to control things such as LED brightness, cooling fan speed, and simple sound producing devices.

The CPLD’s architecture gives it another useful capability for I/O expansion, the ability to accept inputs and drive outputs at different voltages. This multi voltage capability is often utilized for another common application; the communication bridge.

Bridges

CPLDs are often used as a bridge between one or more bus protocols, potentially at different voltages. They can support

  • serial to serial
  • serial to parallel,
  • parallel to parallel

They can even be used to drive an LCD. Because of their simple architecture, they have a low pin delay, making high speed synchronization possible.

Power Management

Another one of CPLD’s features is that they retain their programming and will boot within 500 µs. This means that the CPLD is the first programmable element to wake up on power up, so that it is awake and ready to manage the power up of power supplies and programmable devices ensuring they start in the right order.

Safety Systems

Because of the CPLDs simple architecture and 100% deterministic behavior CPLDs are often used in safety critical systems. One example application is to monitor interlocks, ensuring that the system is in a safe condition before the system can begin operation.

CPLDs pack a lot of capabilities into a compact package, they can reduce PCB complexity and allow reconfiguration on the fly. If you have never considered a CPLD in your design, the designers at PNC can help you with the CPLD circuit design, CPLD programming and Circuit board fabrication. Talk to PNC today.

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Printed Circuit Board thickness considerations and requirements

How Do You Select a Printed Circuit Board Thickness?

Selecting the correct PC Board thickness for your product requires balancing of three often competing aspects of the design: manufacturability, electrical performance and mechanical constraints. Modern PCB fabrication techniques at PNC give the PCB designer great flexibility in specifying the PCB lamination stack-up and gives them the option to design a PCB in a thickness other than the typical choices of .031”, 062” or .093”.

Manufacturing considerations in selecting a PCB thickness

To understand how to specify PCB thickness, it is important to understand how PCBs are fabricated. Most multilayer PCBS from 2 layers to 40 layers are constructed of these three basic materials.

  • Core – a fully cured fiberglass panel usually with copper foil on both sides. It is essentially a two-sided Printed Circuit Board. PNC stocks cores in a variety of materials and thicknesses, down to 3 mils thick.
  • Prepregs – fiberglass sheets impregnated with uncured epoxy resin. This resin will cure and harden when subjected to heat and pressure during the lamination process. It is the functional equivalent of double-sided tape. PNC also stocks prepregs in a variety of materials and thicknesses.
  • Copper foil – used to create conductive layers. Copper foil thickness is chosen by the amount of current the traces in each layer of the board will need to carry.

Multilayer boards can be manufactured in a variety of thicknesses by mixing standard core thicknesses with standard prepreg thicknesses. The lower limit of PCB thickness is set by the number of layers and the minimum available core and prepreg thicknesses. Copper foil thickness also plays a small role in overall PC Board thickness.

Providing you want to stay with the standard thicknesses, I’ll give you an example of PNC’s standard core thicknesses based off the core copper thickness. Let’s take an .062 and compare the stack-ups. See Figure  below:

Stack-up for an .062 multilayer:
062 thick PCB (002)

 

 

 

Notice to achieve the .062 overall thickness, the core thickness needs to be compensated based on the copper weight of the design. When using 1 oz copper we would use .038 core and .035 core for 2 oz. Also, the amount of pre preg would need to be adjusted as well to get to the thickness required. This is just one example when trying to determine overall thickness of your PCB.

The maximum PCB thickness is usually governed by something called the drill aspect ratio, which is the ratio of a drilled holes depth vs its diameter. When a hole is drilled, the deeper the holes becomes the harder it is to guide the drill accurately (because the drill deflects as it is pushed through the material) until you eventually reach a limit where you can no longer guarantee that the resulting drill hole will be centered in all the pads through the PCB. This is also referred to as drill wander in the PC Board fabrication world.

The aspect ratio for a through hole is the (board thickness) / (drill hole diameter).

Typically, the ratio is limited to approximately 10:1 This means that for a .062” thick board the smallest through-hole drill size is .006” which is the minimum drill size available at PNC. For a .093” thick PCB the smallest drill hole size will be .009” As board thickness increases, more complex via creation techniques such as laser drilled microvias are required to maintain the required pad density under components such as BGAs.

PCB thickness considerations for high speed circuits

One of the assumptions an electrical engineer makes when designing a circuit is that the PCB itself does not contribute any impedance to the circuit. However, in high-speed PCB design the integrity of the signals is definitely affected by the physical characteristics of the PCB.

Unfortunately for the designer the primary sources of parasitic capacitance and inductance of a PCB are affected by board thickness in conflicting ways, forcing the designer to carefully consider the trade-offs.

Vias

PCB vias can introduce both inductance and capacitance to the high-speed circuit. Parasitic inductance and capacitance of a via both increase proportional to board thickness.

Capacitance between layers
The capacitance between traces on different board layers or between traces and the ground plane are inversely proportional to the thickness of the dielectric between them. More space between layers will reduce parasitic capacitance and ensuring that all high-speed signal traces are the same distance from the ground plane will help impedance matching between them.

Crosstalk

Crosstalk between signal traces can be minimized by routing the PCB traces further apart and reducing the dielectric thickness between PCB trace and reference plane.

Mechanical Constraints

A PCB is ultimately a mechanical component of the product and is therefore subject to a variety of mechanical constraints. The PCB or PCBs must fit within the product envelope. This often requires that a PCB be as thin as possible. On the other hand, PCBs are subject to the torqueing forces from cables connected to the board edge and external connections. Preventing board failure during assembly or in use requires a circuit board fabrication thick enough to withstand these forces.

Finally, PCBs in the field are subjected to both vibration and shock. For example, large PCB panels can vibrate in several different modes when subjected to vehicle vibration, causing fatigue and eventual failure of solder joints. The rule of thumb is to get the resonance modes of a PCB to be 10X the input vibration. This requires designing thicker, stiffer PCBS and by careful placement and design of the PCB mounts.

These are the three most important considerations in selecting a PCB thickness. To optimize a PCB design, the PCB designer needs to understand all of these requirements and constrains on the PCB lamination stack-up, and have the flexibility to choose a PCB thickness that balances these often conflicting constraints. The team at PNC can help you design a PCB that meets your needs at a competitive cost and lead time.