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HOW DOES SMT ASSEMBLY WORK

HOW DOES SMT ASSEMBLY WORK?

While modern designs for electronics get smaller, more designers depend on the technique of surface mounting. After the 80’s, this technique became famous and hasn’t stopped being the dominant PCB assembly technology for electronics production.

Almost all of the devices in your pocket – either an iPhone xs max or a smartphone – has probably been produced using surface mount technology (SMT). Most of those components in your vehicle or Transportation today have probably been assembled using SMT.

PCB assembly
PCB assembly

What is Surface Mount Technology (SMT)?

Assembling electronics with SMT involves assembling electrical parts using automated equipment that places components on the printed circuit board (PCB).

Manufacturing devices using surface mount technology (SMT) essentially imply electronics assembly using machine tools. In contrast to traditional THT procedures, SMT elements are put directly on top of the PCB rather than soldered to a radial or axial lead. SMT has been the most commonly utilized method in the business when it comes to ethernet interfaces.

Placement and Assembly of Components:

The components to be assembled are inserted into the pick and place feeders or trays. Intelligent software applications guarantee that components are not unintentionally swapped or misloaded during the config file. The SMT pick and place machine then autonomously takes each part from its tray or reel using a pressure pipette and puts it in its proper location on the panel using accurate X-Y cross pre-programming. Our equipment can assemble up to 24,000 parts per hour. Just after SMT assembling has been finished, the PCBs are transported to soldering reflow ovens.

Soldering Components:

The reflow-soldering technique is utilized for series manufacturing orders. This method involves placing PCBs in a nitrogen assisted environment. It is then progressively heated with hot air when the solder paste melts, and the flux vaporizes and attaches the parts to a PC Board. The panels are cooled down after this step.

SMT ASSEMBLY
SMT ASSEMBLY

Solder Paste Usage:

A few of the initial stages in SMT manufacturing is the administration of the solder paste. Solder paste is squeeged through aperature openings in a stainless steel stencil.  Once the squeegee passes over the stencil, the PCB is lowered and travels to the next operation, solder paste inspection, known as SPI. After the solder paste has been verified, the PCB’s move to the SMT pick and place machine.

AOI System in SMT:

AOI visual inspections should be carried out for virtually all manufacturing orders in verifying the quality of completed panels or to capture and rectify an error. The AOI section analyzes each Printed circuit board with multiple cameras and analyzes the look of each circuit to the proper, pre-defined sample image. They will either fix the error or remove the panel from the device to examine it further. The AOI visual management guarantees consistency and precision in the manufacturing process of the SMT assembly.

SMT Components that are not Suitable for Auto Pick & Place:

While most components are placed automatically, others are not installed. This can be for several reasons. Some of them are,

Ø Thermal stress:

Other circuits may be too resistant to thermal and are not perfect materials for soldering reflow temps. These materials must be installed manually to protect them following the usual assembly procedure.

Ø Too light:

Specific components are not substantial enough and, consequently, have a low bulk ratio for conventional soldering automated placing equipment.

Ø Rugged solder joints:

Many components, like connection leads, require a stronger solder joint. Some components are soldered manually to enable this.

This enables rapid examination and repair of components that may be at risk of layout for infringements before the soldering oven is passed.

Surface mount technology benefits:

As with cross-holes, both advantages and drawbacks are included with SMT. Let’s start with some SMT design advantages:

1.   Efficiency:

Thanks to SMT technology, designers can now transform complicated circuits into smaller PCB’s.

In contrast with using the storage on a PCB more efficiently, the SMT board is quicker to increase its overall capacity.

2.   Fewer mistakes:

SMT assembly is very reliant on technology and not so very dependent on people. SMT is a far less error-prone procedure since it’s nearly fully automated.

3.   Cost Accessibility:

These are some of the reasons for the SMT module was to reduce cost. SMT needs far fewer holes in the circuitry. This substantially reduces manufacturing and handling expenses. Furthermore, SMT is much more able to produce large quantities, thereby improving the unit cost.

SMT Disadvantages:

As with other production processes, SMT design has certain drawbacks. The most important is that it needs considerably more eye for detail than a complete construction. Even if the process is substantially automated, your specifications must still be fulfilled to create quality. This is mainly the responsibility of the inventor and the producer of the electronics equipment.

There may also be problems when SMT can be used to put parts on a PCB that works under circumstances that include:

  • Machine stress
  • Ecological stress
  • Stress of temperature

This issue may be addressed by mixing SMT with complete processes to achieve both advantages. That’s correct — on the very same pitch, you may utilize both!

What is the SMT-SMD Difference?

The distinction between SMD & SMT is that SMD relates to the electronic element placed on a Board. SMD is an integrated circuit.

Surface mount technology (SMT) refers in contrast to the way electrical components are placed on a printed circuit board.

SMT refers to Surface Mount Technology and is the complete technology used to place and solder electronic parts on printed circuit boards or PCBs such as resistors, condensers, transistors, electronic components. The devices utilized are also known as surface mounting devices (SMD), surface-mount devices. It should be pointed out that SMT does not have to preserve for constituent pins utilizing holes, and SMD is considerably smaller than by-pass technology.

SMT features:

  • Parts do not have connections or short leads alone;
  • On the same edge of the PCB, the top part of the device and the solder joint;

SMD features:

  • miniaturization;
  • No plumage (flat / short plumage);
  • authoritative Parenting for PCB assembly mounting;

Uses of Surface Mount Technology:

SMT mounting was developed to produce a better, more robust electrical product.

Many typical uses for surface mounting technology are shown if you look around your workplace or home area. Anytime you need a commodity, turn to the surface mount Device structure:

  • Shorter
  • Thinner
  • Faster
  • Most potent

While an SMT assembly is still utilized in some situations or even in specific places aboard.

Summary:

Utilizing the surface mounting technique for electronic engineering, electronic modules are integrated using automated machines which put various elements onto a PCB.

Contrary to typical technological procedures, SMT components are put directly on the surface of the printed circuit board rather than soldering to a lead. Although an SMT device may seem quite complex, it operates extremely fast. The base of the SMT machine utilizes a tiny vacuum head to collect the parts before putting them accurately in the circuit. These devices, known as “pick” and “place” devices, pick up bits from a periodical and position them on a vacuous circuit board. It is important to remember that the correct programming of these devices plays a significant role in efficiency and durability.

ICT Testing VS Flying Probe Testing - PCB Assembly

ICT Testing VS Flying Probe Testing – PCB Assembly

PCB Assembly
PCB Assembly

Flying Probe testing and In-Circuit Testing (ICT) are excellent choices for testing the quality of circuit board construction. Both tests detect the expected problems before the circuit board gets into mass production and assemblage. Both tests are a fantastic way of assessing your end product.

Testing of Circuit Boards:

PCBs are getting progressively advanced to fulfill the technical requirements of our digital era. Automatized testing of a board before the mass manufacture permits you to find out faults before mass manufacturing. In-Circuit Testing (ICT) and Flying Probe Testing can assist you in finding out these fundamental issues in the examining process:

  • Bonding Problems
  • Lamination
  • Copper Quality
  • Hole Wall Reliability
  • Electric conduction
  • Electrical resistance To Environmental Factors

In-Circuit Testing (ICT):

In-Circuit Testing equipment can find out 98% of PC Board constructing problems and is among the most best-selling options. It functions by placing the electric circuit board on the mend with a series of investigations to examine the different characteristics of the circuit board. It cannot just check for constructing defects but also operation functionality.

In-Circuit Testing is an effective instrument for PCB testing. It applies a bed of nails in-circuit examination equipment to approach the circuit knobs of a circuit board and determine the performance of every part. It can also test a few functionalities of digital laps, though the complexity attached can make it economically preventative.

In-Circuit Testing is most appropriate for testing productions that are more highly developed and high-volume. All the same, the up-front prices and growth lead time with IC testing are more advanced and more durable, respectively, than those of flying probe testing (FPT). This is as your producer must expressly create a customized IC testing fixture for every PCB.

The bang-up thing with IC testing is that after the instrument is formulated, costs per unit incline to be more down than with flying probe testing (FPT) as it entirely takes approximately 1 minute for a single test cycle. Flying probe testing (FPT), it can take up to 15 minutes per circuit board.

Flying Probe Testing (FPT):

Flying Probe tests (FPT) are some of the times known as “fixtureless in-circuit tests.” They yet utilize probes to try out lineaments on the PCB, but rather than a fixture, the investigations run to the test dots thru a programmed software system. Hence the examination “aviates” where it is required. This choice is most beneficial for low-volume and PCBs yet in maturation because of its versatility.

Contrary to an IC Testing machine, Flying Probe Testing (FPT) does not use a bed of nails mend. As an alternative, it utilizes a small quantity of portable and fixed probes to make a well synchronic in-circuit test of the big top and bottommost of your Printed Circuit Board. It is manufactured of high-precision goads — a few machines utilize as a couple of as 4 goads, although others can use as much as 20 per PCB side. They are programmed to adjoin component pins and execute electrical and operational tests to check if the circuit board is sound for the field.

Flying Probe Testing (FPT) is most appropriate for products that are in the immature stages of evolution and are low-volume grades. It needs no traditional tooling, and customization for each PCB is followed through programming utilizing the CAD data files you provided to the maker. With flying probe testing (FPT), costs-per-unit are more advanced equated to in-circuit testing because of more elongated test round periods per board (about 15 minutes)

In-Circuit Testing vs. Flying Probe Testing:

They both are good in their way, but they both have slightly different properties for testing circuit boards. In-circuit testing vs. flying probe testing depends on the following factors.

  1. Product pattern:

An effective quality test program (also recognized as adequate ‘coverage’) will count the choice of your Computer-Aided Design (CAD) data files and schematic drawings.

The CAD information file is utilized to bring forth the standard test program, which assures that data is sourced from the master design instead of any blue-collar interpretation of additional data. Good choice of populated and unpopulated sample PCBAs are essential for calibrating the test programs, ‘debugging,’ and creating any mends, so the assemblages physically accommodate as they were specified. Therefore thinking about product pattern for a bit, what are the main differences between each examination solution you might prefer to keep in mind?

  • In-circuit testing will need at least a 50 thou broad test pad per net, which has been organized into the PCB direct and utilized to aim for the determined test investigation. Double-sided mends can be expensive, so these had better, ideally, be on the same side entirely of the PCB.
  • Like those proposed by some other companies, flying probe testing machines can examine the ends of parts, pads, and exposed vias to get an approach to the electric network mesh.
  1. Coverage:

As we discuss ‘coverage,’ we look up to how much of the electric circuit you are competent to test. Both in-circuit testing and flying probe testing follow out what is known as a ‘manufacturing defects analysis’ or MDA, which permits the absolute majority of the most mutual process defects that are expected to fall out. These can let in: open electric circuit (due to depleted or defective soldering), short electrical circuits, resistless component measurements (resistances and electrical condensers), junction rectifier and electronic transistor orientation, and standard supply electric potential measurements. , given that these components are mutual to both testing programs, what puts them apart?

  • In-circuit testing can also provide restricted analog and digital measuring, which flying probe testing cannot due to the restricted number of investigations.
  • In addition to the vector-less examination, ICs that are integrated circuits can include a few powered (albeit familiar) operational testing to ascertain the soldering of flags to the PCB Assembly by a non-contact capacitive investigating or plate. In many cases, flying probe testing is restricted to just vector-less tests.
  • Almost all flying probe testing systems will propose a few forms of restricted optical inspection, which adds up coverage for those factors that cannot get at electrically. In-circuit testing mends usually will not offer the choice of optic inspection.
  1. Cost:

The programming cost will hinge upon the complexity of the assemblage but is generally as-is for either test result, potentially about £2000 more or less. As it comes to additional charges affiliated with the test, all the same, there are a few significant differences to have in mind:

  • The fixture prices of flying probe testing are typically zero, but in-circuit testing mends, in contrast, can flow to an extra of about £4000.
  • The evolution lead time for the flying probe testing is generally less than 7 days, but in-circuit testing can have up to 6 weeks for mending, construct, and programming.
  • In the consequence that your product pattern alters in any case, it will just need a program alteration. In the case of in-circuit testing, it could quickly require a new mending if any part or examine pads have been affected.
  • The actual machine test time is generally less than 60 seconds, which signifies that it is perfect for working promptly through bigger batches. At the same time, flying probe testing can accept a lot of minutes, which intends that it is often more suitable for little sets.
  • The velocity of in-circuit testing also means that it is comparatively cheap, frequently coming in at lowers than £1 per unit. Whereas flying probe testing is a somewhat more tedious process, and so can cost about £50, or more, per assemblage.

Final Words:

On the whole, the option between In-Circuit Testing and Flying Probe Testing will hinge upon many essential components of your project. Mainly these include:

  • Anticipated masses
  • PCB pattern/complexity
  • Budget
  • Lead evolution times

While making the PCB contract with the manufacturer, you should have a perfect understanding of every test system, which will only be better for your particular needs. For more small-scale circuit boards that do not need a lot of examination or circuit boards acquired in low masses, the flying probe testing system might be the most beneficial option. On the other hand, enormous groups of circuit boards and composite boards will require the velocity and extended capacities of in-circuit testing.

Frequently, printed circuit boards manufacturers will practice a combination of both testing systems to present you with the most effective results. As flying probe testing will be utilized for standard testing during the image stage of the circuit board development, so will transition the volume of the testing system to the In-circuit testing system for the entire production.

Merely by keeping in mind the expected benefits and the basses of the in-circuit testing vs. flying probe testing, is difference between the two programs, you should experience a much better ordered to choose the best testing scheme for your PCBA assemblage and both testing services are available at PNC.

Contact us at sales@pnconline.com to fulfill your customized testing requirements.

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.

Minimizing Crosstalk in PC Board Layout

Minimizing Crosstalk in PC Board Layout

In this ongoing series on PCB layout from the design team at PNC, previous posts have looked at some of the initial steps to turn a circuit schematic into a manufacturable, reliable PCB. These posts have looked at  component placement, selecting appropriate trace widths, and BGA routing.   In this post we are going to take a deeper dive into methods for reducing crosstalk in the PCB design. After the power and ground have been routed, the next task is to route high speed signal traces, and the traces that could either generate or receive crosstalk.

 What is Crosstalk?

Crosstalk occurs when the signal on an aggressor trace on a PCB appears on a nearby victim trace, due to capacitive and inductive coupling between the two traces.  Typical aggressor signal traces are:

● High speed digital signals, especially clock signals
● Noise from switching power suppliers
● High frequency RF.

Victim signal traces, on the other hand, carry high impedance signals like op amp input lines or reset lines, or low impedance signals with long loops.   Low amplitude signals such as a sensitive analog measuring circuit traces are also susceptible.

Crosstalk occurs when aggressor trace and victim trace are close together and run in parallel for a distance.  The aggressor and victim(s) can be side to side on the same layer or on top of each other on adjacent signal layers. Coupling between traces on adjacent layers separated by just a thin section of laminate is called broadside coupling.

Minimizing Crosstalk in PC Board Layout
Minimizing Crosstalk in PC Board Layout

 

 

 

 

 

Printed Circuit Board Design guidelines to reduce crosstalk

There are several design rules to reduce crosstalk between signal traces.  Before applying these rules, the first step is to use the general guidelines described above to identify and flag any potential aggressor signal traces and their potential victims.

Since crosstalk occurs between two traces running in parallel, try to reduce the distance that the aggressor and victim traces run in parallel. Unfortunately, this may be difficult if the signals originate and terminate from the same locations.  To minimize broadside coupling try to orient the signal traces east-west on one layer and north-south on the second layer.

It is essential to have a broad contiguous ground plane directly under (or over) the signal layer.  A ground plane located between two signal layers can prevent broadside coupling. However, make sure that ground planes located on adjacent layers but not electrically connected do not overlap.  The overlapping ground planes separated by a dielectric form a capacitor, which can transmit noise from one ground plane to the other. This can defeat the purpose of separate ground planes if they were created to isolate the noisy elements of a circuit from the noise sensitive ones.

Increasing trce spacing

The most effective method of reducing crosstalk is to increase the spacing between the aggressor signal trace and the potential victim traces.  Like all electromagnetic radiation, electrical or magnetic coupling between the two traces drops with the square of the distance between them.  The amount of spacing required between the traces is dependent on the height of the traces above the ground plane.   The formula defining this relationship is from Douglas Brooks “Crosstalk Coupling: Single-Ended vs. Differential”   The coupling between two traces is proportional to:

Where S is the spacing between traces, and H is the distance from the trace to the ground plane.  Once H is defined by the lamination stack-up, the relative change in coupling can be easily plotted as a function of S.  Douglas Brooks looks in detail at the coupling between traces under several scenarios.  For those looking for some general guidance, a spacing of 5H is considered conservative.  The PC Board design team at PNC can assist designing a PCB stack up that will minimize the spacing needed between coupled traces, ensuring that crosstalk is minimized while maintaining routing density.

Finally, for very high speed digital signal traces, consider the use of differential pairs.  For many designers, the most common applications for a differential pair is for a high speed serial bus like USB, SATA, or HDMI.  The design rules for the layout of differential traces is beyond the scope of this post.

The most important part of reducing crosstalk in your PCB design is to first recognize in which signal traces crosstalk is likely to occur, then follow the guidelines above to minimize it.  PNC’s Printed Circuit Board designers have experience with high speed digital and RF circuits and can help you select the correct PCB layer stack-up and review your designs for areas where crosstalk is likely and suggest ways to minimize it. Request a design review from PNC today