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ICT Testing VS Flying Probe Testing - PCB Assembly

ICT Testing VS Flying Probe Testing – PCB Assembly

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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.

Advantages of Laser Cut SMT Stencils for SMT Assembly

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Laser Cut SMT Stencils:

Surface mount technology or SMT Stenciles is the procedure of mounting the electrical parts straightaway onto the PCB surface. SMT has replaced the through-hole technology technique of aligning parts with cable heads into holes in the PCB. The essential part of the SMT procedure is the covering of solder glue on the PCB. First, it is managed by screen impressing the solder glue with the assistance of solder stencils. Then, the solder glue is equally applied with the utilization of a squeegee.

Laser Cut SMT Stencils are laser-cut solder glue image stencils. It is organized for hand-operated solder glue impressing applications. These stencils are frameless, and it expeditiously eliminates the tiresome hand bonding of PCBs. Utilizing image stencils, you will be able to create your image on PCBs using your Gerber or CAD data file.

Five amazing properties of Laser Cut SMT Stencils:

  1. Laser-cut SMT stencils are created by utilizing the CAD data file that you provide. You can give a Gerber file for this as well. These data files are a two-dimensional graphic representation of every layer of a PC board where pads, vias, and tracks are presented with the assistance of different lines and figures. It depicts the electrical circuit board pictures, letting in the copper layers, legend; solder mask, drill information, and many more. These data files, either CAD or Gerber files, assists in producing the SMT image stencils for constructing a PCB board.
  1. Laser-cut SMT stencils typically bear a frame. Besides, it comprised of a sheet of stainless steel, in which the apertures are adequately organized. Utilizing it, they can squeegee the solder paste onto the PCB. Hence, it keeps the application of solder paste on amateur surfaces.
  1. The Laser cut SMT stencil generally is used on an full auto or semi auto screen printer using a squeegee blade. These blades traverse over the foil to deliver the potential paste volumes on the Printed Circuit Board surface.
  1. The laser-cut SMT stencils are usually stainless steel. It is utilized to assist the PCB operator in depositing glue or paste, onto the PCB surface. Steel stencils are more long-lasting and accurate than polyimide stencils. Often, other materials like mylar and nickel are used as well. Richly nickel substance stainless derivative has little grain, backing up better release attributes as the aperture surrounds are smoother. Precise release of solder paste through the aperture is essential. Additional solder paste deposition can make solder bridging. Lower solder deposition can make fragile solder joints that can involve the operation of the PCB.
  1. Laser-cut SMT stencils are laser-cut solder stencils. The laser-cut constructing technique improves the aperture definition and best dimensional leeways for more effective pitch apertures on the stencils. Hence, you will be able to have the best quality print with most minor faults. Laser-cut SMT stencils keep a precise and quotable solder deposition procedure. To utilize the laser-cut SMT stencils, set the PC board into the circuit board holder. Adjust the image stencil over the PCB SMT pads. Set the solder paste on the image stencil and disperse it through the whole width of the hole squeegee. Apply a squeegee to roll the solder paste over the image stencil coercing the solder paste through the image stencil on the PCB board surface.

 Advantages of Laser Cut SMT Stencils:

There are numerous advantages of Laser cut SMT stencils. Like:

  • Laser-cut SMT Stencils eradicates the mistakes that are expected to fall out in the hand soldering of image electrical circuit boards. The perfect laser-cut apertures enable fluent aperture sidewalls, hence bettering paste transfer. In addition, they are permitting post-processes of electropolish and nickel-metal plating to create the aperture walls articulate.
  • As laser-cut SMT Stencils are usually frameless, it reduces space requirements. Furthermore, it is significantly cheaper than framed image stencils.
  • These laser-cut SMT stencils are not glued in a frame, allowing optimal solder paste volume control.
  • Laser-cut SMT stencils can present fantabulous print performance and better the quality of your image Printed Circuit Boards.
  • Laser-cut SMT stencils are specifically organized to avoid the odds of whatsoever fault while using the solder paste on the PCB board. It also easy clean-up of the solder paste from the surface of the electrical board for quotable and precise solder paste deposition.
  • Laser-cut SMT stencils allow quick assembly with minimum cost. It brings down the PCB image assembly time. It is low-priced, concise, easy to handle, and easy to dispose of or recycle.
  • Laser-cut SMT stencils have a 24-hour turnaround standard.
  • Laser Cut SMT stencils have smooth inward pad walls, with geometrical fence changes of fewer than 3µm for best glue release features.
  • These stencils have aperture consistency for a decrease in expected defects.
  • These stencils have high pad positional conciseness for utmost good pitch accuracy in impressing. Tolerances of about 5um are possible with modern lasers.
  • Contrary to chemically engraved stencils, these stencils to Printed Circuit Board registration boast an exemplary circuit board to stencil registration.
  • These stencils have hyper delicate pitch designs less than 250µm can be recognized without problems letting you impress today’s challenging and outstanding pitch devices.
  • This stencil’s high accuracy of land visibility sound reflection in the stencil permits you to make an easy and authentic stencil position on PCB.
  • These stencil fabricating is performed straightaway from CAD/CAM data files eradicating problems with photo tool projecting and fictionalization quality and the caliber of surface planning and photoresist application to the queer as it is the same case with chemical engraving technique of stencil manufacturing.
  • These stencils bear chromium steel serving as ground material for these stencils has a high-potential rate. Hence, the stencil does not alter in size, and the aperture design is not disingenuous even after 10,000 impressing cycles that making the chromium steel stencil very authentic in usage.
  • Its smooth walls and pointed aperture profile. It was step-up the possibility of solder glue to pass over stencil apertures during every print cycle.
  • The laser-cut SMT stencils are easy to assemble and utilize.
  • These stencils create high-volume; chromium steel stencils are handy as they have a long span of life, allowing multiple utilizations for solder glue applications.
  • These same stencils permit you for on-contact and off-contact impressing on PCBs.
  • These laser-cut SMT stencils are efficient when utilized for multi-level impressing of PCBs.

How to check the size of the stencil?

The laser-cut SMT stencil size is compiled into 2 parts: inward size and general size. Inward size is the size well-matched, and that of PC Board set up to be collective, although overall size concerns the size well-matched with printer parametric quantity limit. As far as both sizings are precisely designed, the stencil will draw total usage of its functions.

Inward size of laser cut SMT stencil can be worked out adjusting to the following rule:

  • Width of Frameless stencil = width of PCB + 200mm while its Length = length of PCB + 200mm
  • Width of Framed Stencil = width of PCB + 100mm while its Length = length of PCB + 100mm

For instance, if one electric circuit board measure in size is 50*50mm, then the sizing of its bordered stencil should be about 150*150mm, and the sizing of its frameless stencil had better be about 250*250 mm.

It is comfy to remember and function, so it worked out for hand-operated solder glue printing in laser cut SMT stencils assembly before the coming of automatic printing machine. It can tell that different PCB sizings lead to propagations of different inward sizes of laser cut SMT stencils.

It derives from an automatic solder glue printing machine, all the same, relatively strong. The general size of these laser cut SMT stencil has to be ascertained by the parametric quantity limit of the printing equipment, that is, the printing machine, because stencil has to do work within the scope of printing machine with a frame. Diverse printing machines feature different parametric quantity rules. According to the conducted research, the stencil size congenial with our printing machine can be 650mm*650mm or 736mm*736mm.

PC Board designers have to focus on the internal size of the stencil; they don’t need to care about its overall size since it is generally determined by the parameters of the printer in your contract assembler workshop.

Final Words:

The laser-cut SMT stencils had better enable you to resolve your printing troubles to alleviate the PCB fabrication and assembly process. These stencils are well-suited for image fabrication, and the flapping helps keep the glue in an enclosed area during the impressing process. Furthermore, these stencils’ better accuracy saves time, and of course, step-ups yield. These laser-cut SMT Stencils are close-packed and easy to deal with. As an outcome, it has acquired popularity in offering faster and cost-efficient PCB prototyping.

These laser-cut SMT stencils that are decently designed enable highly effective PCBs that are uniform and quotable. This not just assists in saving up costs in the end, but it will also permit a higher-quality ultimate product. The team of highly competent technicians designs all the laser-cut SMT stencils with superior precision to assure you get the complete products that meet your requirements.

At PNC, you will get your design SMT Stencil’s requirements fulfilled at an affordable rate.

3D Automatic Optical Inspection (AOI) for PCB Assembly Introduction

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The highest demand used in quality management of electronic printed circuit boards (PCBs) and PCB assembly is automatic optical inspections and automated optical inspections (in short, AOI) (PCBA). AOI inspects the electronic assemblies such as PCBs mechanical visual inspection to ensure that the components of PCBs are in the right place and the contacts are correct.

Automated optical inspection (AOI) is an intelligent visual inspection of the production of the printed circuit board, where all catastrophic failures (such as broken components) and quality faults can be scanned automatically by a sensor.

It is widely used in the production phase because it is a way of testing without touch. It ensures the multi-layer circuit boards provide a high degree of durability.

For the following various applications, it is essential:

  • Infringements of line spacing
  • Violation of spacing
  • Copper excess
  • The shortage of pad
  • Short circuits
  • high frequency
PC board
PC board

What does AOI inspect?

AOI is a primary method used to build and test electronic printed circuit boards and PCBs for automatic or automatic optical inspection. Automated optical inspection, AOI allows quick and precise assessment of electronic assemblies and, especially, pcb assembly to ensure that the standard of goods is good and that the object is appropriately and without processing defects.

What is the need for AOI inspection?

Current circuits are much more complex than boards were a few years back, notwithstanding the significant changes that have been developed. With the advent of surface mounting technologies and more size decreases, boards are exceptionally lightweight. Even comparatively ordinary panels have millions of fused joints, and most issues are observed.

This growth in board difficulty also implies that manual examination is currently not a feasible choice. Even if the solution was approved, the inspectors quickly fatigued it, and poor and wrong design was easily overlooked. With great demand, high-quality goods on the market now require very simple, very stable, and fast.

To ensure that the product quality continues to be good, methods are required. AOI is an indispensable instrument within the context of an advanced electronic test plan, ensuring that the expense is held to the lowest possible levels by identifying faults at an early stage of manufacturing.

Benefits over manual visual inspection

PCB devices switch to ultra-thin, lightweight, higher densities, and exemplary size components. The part assembly width of the circuit board has increased, the width and distance of the Printed Circuit Board -line and the pad are decreasing and reaching the micro-level. The manual process of visual examination cannot be achieved. Furthermore, people seem to be tired and emotionally affected, according to the textbook. Inspection equipment is more stable, repeatable, and precise when it comes to machine vision.

Manual visual examination is a vital part of our BES operation. All new boards, either we order from a new supplier or a well-experienced BES company, are visually inspected by us. From solder masks to solder joints, we test all on the floor. Shipping packaging is also evaluated. When we develop our projects, manual visual testing is also helpful throughout the development, from designing to large-scale production. It was the first phase in our identification and repetition of design or manufacturing problems.

  • The usual general information SMT operator will fit well for quick and easy manual visual inspection.
  • Manual visual inspection with high flexibility;
  • The original costs are minimal, and only the initial Labour costs are spent, and high expenses are not available;
  • Preparation is fast.

How can time save done from the visual inspection process?

Visual inspection proves to be a game-changer, with many apps in almost every domain. The company is now moving into manufacturing and production, enabling them to use the power of profound learning and thus have quicker, safer, and superior automation.

  • More quickly

CPU speeds, as calculated in FLOPs and even accurate measurements, result in observations and conclusions, which are done incredibly quickly.

  •  Accurate

An automated machine can standardize the measurement of absolute measurements.

  • Trustworthy

The machine is impartial and programmable as required and without doubt following instructions. It is undoubtedly a result of this technological transition that is moving global producers into different production and productivity levels.

Final Thoughts

AOI is a vital factor in ensuring the accuracy of your completed electronics items is defective and accurate. It gives a shorter timeframe, more efficiencies, and lower prices, which would have increased if reworking was required.

The AOI process provides reliable monitoring and resulting information which enables improved quality control procedures management and the correction of potential issues. The algorithms will monitor the successful and defective PC Board components and record them. Efficiency is also improved from the point of view of process control, organizational integrity, and reporting.

The controls provide search, identification, and measurements or diagnosis for the outgoing product condition. Inspection is an operation. Tasks of supervision have typically been assigned to people. Efforts to simplify industrial inspections to eliminate mistakes and reduce monotony have encountered technical constraints and cost factors of deployment. A prototyping model is an occasional compromise. Reviews have released new study status on manual, hybrid, and automatic inspection.

Perhaps the most critical inspection process is the visual inspection of the parts made. Draw the section and equate the area with the painting visually. For units with several functions, this is particularly relevant. Anything may go wrong, and one of the several production cycles.

During AOI, optical inspection algorithms usually use visual techniques to ensure defects on written platforms. They can identify a range of material removals, such as nodules, scratches, and marks, as well as known dimension faults, such as open circuits, shorts, and solder integrity. They will also spot faulty components, missing components, and parts that have been misplaced. All system is designed to monitor tests conducted by manual operators can be carried out much quicker and more reliably.

How can We (PNC ONLINE) help you in 3D Automatic Optical Inspection?

At PNC, you will get your design checked from two (2) Mirtec MV-6 OMNI machines which itself is high-speed/high-performance 3D AOI MACHINE FIFTEEN MEGAPIXEL CoaXPress Camera Technology. It has an advanced eight-phase Color Lighting System Ten Micron / Pixel Precision Telecentric Compound Lens. It is designed with an Integrated Ten Mega Pixel SIDE-VIEWER® Camera System Precision Closed Loop AC Servo Drive Motor System which is extremely simple to program and operate. It also has 3D Co-Planarity Inspection – Gull Wing Device with an example as shown below:

PCB Assembly
PCB Assembly

We follow all the system parameters and are set up to meet IPC inspection requirements. Get your Automatic Optical Inspection done for your 3D design at PNC. Contact us at sales@pnconline.com

 

Work with PNC to Reduce PC Board Costs

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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.

What’s a HDI Printed Circuit Board?

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HDI stands for High Density Interconnect. HDI PCBs have finer traces and trace spacing, laser drilled micro vias and higher connection pad density. Its two chief advantages are that it permits the use of fine pitch BGAs and it reduces the number of PCB layers required because the finer traces and smaller vias allow more circuitry in a smaller area.

Narrow trace widths mean higher circuit density

At PNC standard PC Board fabrication uses a minimum trace width of 5 mil, with a 5 mil space between traces (5/5mil) PNC’s HDI trace widths can be as narrow as 3 mil with 3 mil spacing.  These finer traces allow 160% more traces in the same real estate. 3/3mil spacing will also allow two traces to escape between pads of a standard BGA, meaning less PCB layers are needed to fan out the pins from the BGA.

Microvias are the enabling technology for HDI

Narrow trace widths used in HDI PC Board are a result of the gradual refinement of photolithography and etching technology.  Microvias on the other hand, are a revolutionary innovation driven by the development of high powered lasers that can be controlled accurately enough to ablate a 3 mil hole through the surface layer of copper and underlying laminate, without damaging the underlying layer of copper.

The minimum hole size for PNC’s laser drilled microvias are 3 mil and the minimum pad diameter for the microvia is 7 mil.  Pads for laser drilled holes can be smaller than for mechanically drilled holes because of the location accuracy of the laser drilled hole.  There is no mechanical deflection of the drill bit to account for.  The laser drilled holes can be fully copper filled and planarized flat, so they can be used as pads for fine pitched BGAs with 0.4mm or smaller spacing. Using microvias as pads allows the signal trace to fan out by going straight down and out to an inner layer of the printed circuit board.

The biggest limitation with microvias is the aspect ratio of the holes.  Where a drilled through hole can have a 10:1 depth to diameter aspect ratio, a laser drill can achieve no more than around a 1:1 aspect ratio.  This means that the smallest microvia can only connect two adjacent copper layers. A larger diameter microvia can penetrate two layers. To connect deeper layers, the designer must stack vias one directly atop another.

Laser drilling of the microvias changes the way PCBs are fabricated and gives the designer flexibility that they do not have with through hole vias.  In a standard drilled PCB, via holes are drilled and plated after the PCB fabrication stack-up is completed.  Because the microvias can only bridge two or three copper layers, the microvias must be drilled and plated at each lamination step.  This means that microvias can be fully buried between layers, stacked or staggered to allow the microvia to connect multiple layers of the stack up.

The major space saving advantage of the microvia technology is that vias can just connect traces that need to be connected, rather than taking up real estate all the way through the PCB the way a through hole via does.

The Printed Circuit Board designers at PNC take advantage of this by locating the power and ground layers at the top of the stack up.  Since all active components access power and ground, sometimes through multiple pins, having the power and ground layers directly below the component layer allows all those connections to be made directly by microvias.  This leaves the component layers and layers beneath the power and ground layers completely unobstructed for signal routing. This has the added advantage of reducing parasitic capacitance because it eliminates the circuit stubs caused by plated through holes.

Two sided boards are typically fabricated with a combination of through holes and microvias.   Though holes can be drilled just through the core, connecting the stacks on the top and bottom of the board from the lowest layer, or through holes can be drilled through the entire stack directly connecting the traces on the top and bottom component layers.

 

HDI PCBs are a necessity when using fine pitched BGAs, but they can also reduce cost on PCBs without fine pitched BGAs because of the reduced layer count.  On your next PCB design, talk to the experts at PNC.  They can help you determine if HDI technology is can reduce your PCB cost by reducing layer count and shrinking the PCB size.