Fiberglass Fabric Styles Used in Laminates

Written by Rush PCB Inc on . Posted in PCB, PCB Fabrication

Eminent PCB fabricators such as Rush PCB Inc. use different types of prepregs and laminates for their PCBs. The manufacturers of these materials offer a number of fiberglass fabric styles. They base their selection on the thickness that the finished laminate or printed circuit board will take. It also depends on the amount of resin that will be present for filling and bonding. They make the specific choice depending not only on building up the thickness, but also on secondary properties such as cost, dimensional stability, CTE control, dielectric constant, and stiffness.

Construction of Fiberglass Boards

Manufacturers begin with fiberglass fabric on a warp beam that contains several thousands of individual strands of yarn rolled over a master beam. These yarns constitute the machine direction the fabric will take, which is also called the warp direction. They then slash the warp yarns, or run them through a solution of lubricants or sizing agents and this protects them from damage during the weaving process.

The actual weaving process begins by mounting the warp beam on the back of a loom, with the fill yarns being inserted as the warp yarns pass through from the back of the loom to its front. Earlier, there were the Draper looms, where a wooden shuttle with the fill yarn would proceed back and forth from one side of the loom to another to insert the fill yarns, while the alternating warp yarns moved up and down in a mechanical frame as it created the traditional plain weave, resulting in a woven or drapered edge.

The newer looms operate on air or water jet, where the jet carries the fill yarns across the loom. Cutting off the fill yarns individually leaves a fringed edge. In the modern looms, a single warp beam can contain several thousand meters of warp yarns that represent as much as a single loom can weave in a week.

Conductor Surface Roughness

After the weaving is over, the electrical grade glasses need to be scoured with an aggressive water rinse, which removes excess sizing from the warp yarns. To remove the balance, they are then heated in an oven at elevated temperatures for a long period. The weaver then treats the fabric with finishing agents such as organosilane that provides a surface that resin systems can wet and bond.

Glass intended for polyimide manufacturing requires application of a high temperature finish such as amino-silanes. This makes the bonds tough enough to withstand the use conditions the polyimide will go through.

Although the finish on the fiberglass fabric is only a very tiny amount of material, it vitally affects the way resin will wet the surface during the prepregging process. Poor scouring, heat cleaning, or inadequate silane treatment can leave the prepreg with repellent streaks or spots that often show up when heated. Glass weavers offer a variety of finishes, and the correct choice of finish for each resin determines its performance critically.

Also Read; How to Choose Professional PCB Prototype Assembler

Green Epoxy

Several epoxy resin systems are green in color. This started with fiberglass finishes that had chromium chemistry as their base with the trade name of Volan, which produced a green finish. Now, very few manufacturers use Volan, and use organosilanes instead. However, the complaints from end users about the change in appearance of their product have forced the suppliers to start dying their FR-4 products green to make them look same as before. That explains the reason for green being so common a color for epoxy printed circuit boards.

Smooth resin rich surfaces offer a better fill for internal etched copper patterns. This is often a result of lightweight fabrics with high resin content. Using heavier fabrics result in lower cost, while offering enhanced dimensional stability and permit building up greater thickness at lower cost per mil. However, the use of heavier fabrics usually affects drilling characteristics and surface smoothness. Although thicker and heavier fabrics result in low-cost rigid laminates, they can deflect small drill bits causing them to break.

Warp, Fill, and Direction of Weave

For a woven fabric, the term warp indicates the direction of the length of the roll, while fill indicates the direction of the yarns that fill in from side to side in the weaving process. In commonly used fabrics, the tensions and the number of yarns are not evenly balanced and that has a varying effect on stability and subsequently on registration. For a PCB fabricator, it is necessary to know the direction of warp and fill so they can orient them similarly each time and adjust the processing and compensate for predictable effects.

For instance, for a laminate measuring 36 x 48 inches, the warp is normally parallel to the longer dimension. Unless the customer makes a special request, or it is necessary to cut otherwise, the warp usually follows the longest dimension of a piece of cut panelized or prepreg laminate. When warp is not along the longest dimension, or for square panels, the fabricator marks the warp direction clearly by an arrow on the package or on the material.

Also Read;   PCB Testing: Why is it Important?

Weave Distortion

Under normal handling conditions, warp yarns are under tension and remain straight, while fill yarns should remain at right angles to them. However, for some reason, if some of the fill yarns in the fabric move away from their 90° position, the laminate or multilayer may develop a ripple or twist. For the fabricator, it is very important to have raw fabric with undistorted yarns. However, even for fabric with undistorted yarns, warpage can still occur unless the laminator takes care to align the yarns in one sheet of prepreg relative to another.

Summary

It is not easy to specify or measure the dielectric constant of the laminate, as it depends not only on its intrinsic properties, but also on the method of testing, conditioning of the sample before and during the test, and the test frequency. Moreover, dielectric constant tends to vary with temperature.

At Rush PCB Inc., we determine the characteristic impedance of a PCB based on the laminate thickness, its dielectric constant, and the height and width of the etched line height. Impedance matching and control are critical to linked functional modules when dealing with high-speed devices and designs.

Preventing Delays During Your PCB Fabrication

Written by Rush PCB Inc on . Posted in PCB Fabrication, PCB Manufacturing

pcb fabrication

Delays in your printed circuit board fabrication can be costly and time-consuming.  In today’s world, they are a commodity that there is never enough of.  Believe it or not, there are steps you can take to avoid those dreaded delays during your fabrication process.  We are going to discuss how you can take an active role in ensuring your printed circuit board fabrication runs smoothly and on schedule.

 

Communication

Follow up is an extremely important factor during the fabrication process.  Placing your project at the top of your “things to do list” is a must.  If you are communicating with your fabricator through email, or phone, you must be sure to answer any messages left in a timely manner.  Not answering them promptly can cause an interruption of the manufacturing, especially if a question is being asked or your guidance is needed.

 

Identify Long Lead-Time Parts

You may not realize it, however, some of the parts that are necessary for your project may take up to six months or longer to receive.  Working closely with your manufacturer as soon as you can will help them determine what they order and how quickly they can get it.  Printed circuit board manufacturing is not like shopping at your favorite grocery store, they will not always have the products in stock.

Also Read: Uses of Printed Circuit Board Components & Technology

 

Correct Documentation

You should always keep your product documentation up to date with the correct information.  Speaking with the manufacturer candidly to find out what their specific requirements are is the best way to understand what they need, this way there will not be any confusion.  This will also help eliminate any unnecessary mistakes that will inevitably cause delays in the manufacturing process.

Product Demand Information

Never wait until you are out of (or almost out of) your product.  This only increases stress, time, and cost.  The cost of shipping overnight is much higher than normal shipping methods.  Come up with a way to order your supplies before you run out to avoid additional cost, stress, and time.

Consider a Domestic Manufacturer

Although the cost may be less expensive, you may end up paying a higher cost in the end.  You want to consider the following;

  • Shipping prices will be higher with overseas manufacturers
  • Communication may become more difficult due to time differences
  • The difference in time may also result in the delay of delivery

Find a Manufacturer Who Can Handle the Entire

Manufacturing Process

A manufacturer who can provide their services from start to finish is the most beneficial option for your project.  This saves time because it cuts down on the amount of time it takes to get from one manufacturer to another, be worked on, and then shipped back to the original fabricator.  It makes smarter business sense to keep your product in one place from beginning to end so it can be shipped directly to you.  It also will stop the “blame game” if something is defective you know who is responsible.

Also Read: PCB Fabrication Making a World of Possibilities a Realty

 

 

PCB Fabrication Making a World of Possibilities a Realty

Written by Rush PCB Inc on . Posted in PCB, PCB Fabrication, PCB Manufacturing

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The fabrication or manufacturing of printed circuit boards are the backbone of every computer operated piece of machinery on the market today.  The importance of the PCB should not be overlooked, without it we would not be able to enjoy all of the gadgets that have become a part of our daily routine and important part of our lives.  Just as technology advances so does the fabrication/manufacturing of the printed circuit board.  Chances are that you have benefitted from a PCB in form or the other and may not even be aware it.

Printed Circuit Boards Then

When thinking about PCB’s you may tend to think of what they are today if you are a tech savvy individual.  However, you may be surprised to learn the history of printed circuit board;

  • 1920 they made their debut, they could be made of materials such as Bakelite, Masonite, and sometimes wood.  Holes were made and brass wires were riveted and there you have it!  They were most widely used in radios.
  • 1947 the first double sided PCB with plated through holes was created
  • 1950-60 Advancements in the types of materials that were used to make them although they could only be printed on one side.  In 1956 the U.S. Patent Office granted a patent to scientists.  There process
    • They would draw a wire pattern
    • Photograph it into a zinc plate (creating a plate for the printing process)
    • They would use the plate to print the wire in an acid resistant ink on the copper foil
    • That could be etched by an acid solution
    • 1957 The Institute of Printed Circuits was formed.
    • 1960 Multilayer PCB production began
    • 1960’s and 70’s designers that had good experience would be able to layout and tape boards at a rate of two hours per 14-pin IC on the board
    • 1970’s you began to see changes in the size of the boards which were getting smaller, hot air soldering methods were being used and the RS-274-D was introduced
    • 1980’s Surface mounts were beginning to be used (led to reducing the size further)
    • 1986 saw the release of RS-274X
    • 1995 began using micro-via technology in fabrication
    • 1997 the ODB+++ was released to the general public
    • 2010 the production of Every Layer Interconnect began.

Printed Circuit Boards Now

Today printed circuit boards have evolved and become a part of our modern day technology.  Whether you are wearing a fit-bit, watch, or using an iPhone, the list can go on and on, you are benefitting from there sophisticated, delicate design that keeps the gadgets we depend on running smoothly.  The most exciting part is that this industry shows no signs of slowing down and guarantees new ways that will continue to improve our quality of life and enjoyment of all those gadgets that we can longer live without!  Just imagine what’s to come in the future as we continue to explore the untapped potential of the worlds technology!