Via Tenting, Plugging, and Filling

There are many reasons a printed circuit board designer might want to have a via tented, plugged or filled. First, let’s start with defining these terms since they can be frequently misused and misunderstood.To accurately drill your countersunk holes, we will need the following information.

Via Tenting

This is the easiest and least costly process—actually there is no added cost for this process. Simply remove the mask clearances from the vias you wish to have tented. Tenting a via simply means to cover the annular ring and via hole with solder mask. No special steps are taken to ensure the hole opening remains closed. Tenting a via will sometimes result in the hole remaining covered but it isn’t guaranteed. Smaller diameter vias (12mil diameter or less) have the best chance of remaining closed. The main purpose for tenting shouldn’t be to close the opening of a hole but rather, cover the annular ring to prevent exposure to the elements and reduce accidental shorting or contact with the circuit.

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Copper Thickness FAQ

The most common unit of measure for the copper thickness on a printed circuit board is ounces (oz). But how thick is that? It’s the resulting thickness when 1 oz of copper is pressed flat and spread evenly over a one square foot area. This equals 1.37 mils (1.37 thousandths of an inch). Of course not everyone thinks in mils so please refer to the chart below to convert into your favorite unit of measure.

1 oz Copper Thickness Conversion *To determine the thickness of 4 oz, simply multiply 1 oz thickness x 4.  1.37 mil x 4 = 5.48 mils = 4 oz
1 oz
1.37 mils (thousandths of an inch)
0.00137 inch
0.0347 mm
34.79 µm  (micron/micro meter)

 

Most PCB’s are constructed with 1 oz copper thickness.  At PCB Universe, if we are not given specific specs, we will assume 1 oz when quoting and building your design.  If you have determined that your design requires more current than 1 oz can carry, you’ll need to consider increasing the copper weight or increasing the width of your traces.  Of course the thicker the copper the higher the cost, but there are certainly times where this is necessary.  The cost increase is not only due to the raw material costs but processing thicker copper weights takes more time and is a little trickier to do.  Keep the following chart in mind when designing your board.  The more space you can allow between copper features the better.  Etching the spaces (air gap) between traces is more difficult than etching a trace of the same width as your space.

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Countersink vs. Counterbore

Countersink

A countersink is a cone shaped hole cut into the laminate.  It is typically used to allow the tapered head of a screw to sit flush with the top of the laminate.  By comparison, a counterbore makes a flat-bottomed hole and its sides are drilled straight down.  This is usually used to fit a hex-headed cap or screw.

To accurately drill your countersunk holes, we will need the following information.

  1. Angle of the drill
  2. Major Diameter (finished diameter of the hole at the surface)
  3. Depth the countersink is to be drilled
  4. Which side of the board is the sink on?  Top or Bottom?
  5. The finished diameter of the shaft of the hole
  6. Is the sink and shaft to be plated or non-plated?

Countersink Anatomy.png

Counterbore

A counterbored hole is typically used when a fastener such as a bolt or cap head screw is required to sit flush with or below the level of a surface.

To fabricate your counterbored holes, we would need to know the following information.

  1. Major Diameter (finished diameter of the hole at the surface)
  2. Depth the countersink is to be drilled
  3. Which side of the board is the sink on?  Top or Bottom?
  4. The finished diameter of the shaft of the hole
  5. Is the bore and shaft to be plated or non-plated?

Because the sides of the hole are always parallel, there is no need to specify an angle.

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Controlled Dielectric or Controlled Impedance?

Controlled Dielectric ExampleConfusion abounds regarding the topics of controlled dielectric and controlled impedance in the printed circuit board industry. We’ll try to clarify the subject.

What is the difference between Controlled Dielectric and Controlled Impedance regarding PCB fabrication?
The purpose of controlling dielectric or impedance is essentially the same, to achieve a target impedance on one or more signal lines on a printed circuit board.  For example, your design has a USB signal pair that must have an impedance of 90 ohms (±10%) to function properly. To make sure this will happen, there are many factors that need to be considered and calculated such as trace width, spacing between copper features on the same layer, distance between copper features on other layers, the Dk (dielectric constant) of the laminate used to manufacture the board, as well as a few other factors.  more…

Array Design

Read our latest Array Design Tips article at http://www.pcbuniverse.com/articles.php

The primary reason for having your boards delivered in an array is to make automated assembly faster and less expensive. Running an array of boards through a pick-and-place machine is far more efficient than sending them through one at a time. Arrays are also desirable because they allow the addition of tooling rails, tooling holes, and fiducials, all of which help your assembler.     more…

PCB Universe Latest Press Release

PCB Universe Press Release via MarketWire-New Website Launch

We sent out our latest press release, titled “PCB Universe New Website Is First in Its Industry to Offer PCB Quotes With No Email or Registration-Sign up

Here is an excerpt from it:

PORTLAND, OR–(Marketwire – August 26, 2010) – PCBUniverse.com site has improved the efficiency of quoting and ordering custom printed circuit boards online by allowing users to obtain a quote with no advance registration or required contact information.

[Read the entire press release here]

New Product Launch – Super Value PCB Prototype Service

We are pleased to announce our new product:Super Value PCB Prototype service

We’ve launched our new Super Value PCB Prototype Service ! We offer rock bottom prices on standard 2,4,6 and 8 layer proto boards! Check it out.

Here are the specifications:

Min. Qty. 4 boards Max. Qty. 10 boards * If you need more than 10 pieces it is more cost
effective to order under our standard pricing. Board Thickness .062″ Material FR4 (140°C Tg) Max Square Inches 35 sq”/board Max Dimension 12″ Min Dimension 1″ Copper Weight 1 oz Min Hole Size 12 mil Plated and Non-Plated Holes OK Min Trace/Space 5 mil Final Finish Lead Solder (HASL) Solder Mask Both Sides – Green Silk Screen Both Sides – White Inspection Class II Tooling FREE Electrical Test FREE

There are some restrictions:

Orders must be placed on the Web site with Credit Card File Format Required Gerber 274X (Extended) Drill File Excellon in ASCII format
  • Board outline does not need to be square but should have fewer than 20 edges
  • No Arrays, Scoring, Tab Routing or Perforated Drilling
  • Only 1 part number (circuit) per order
  • No Internal Routing, Slots, Cutouts or Overlapping Drills
  • No Blind / Buried Vias
  • No Counter Bores or Counter Sinks
  • No ITAR Compliance
  • No UL Markings
  • Credit Card Only

Check it out and get a quick pcb prototype quote…there no email or registration required so there’s no reason to take a quick peak. You know you want to…and there’s no one who is going to follow up or try to sell you on something. Just great pricing, great service, and great boards.

How Printed Circuit Boards are Manufactured

Paul Eisle invented the first PCB in 1936. However, it became popular only in the 1950s when the US military started using the technology in bomb detonators. Today, PCB Circuit Boards are an integral part of almost all equipment, like cars, mobile phones, computers and more.

How Is A Printed Circuit Board Manufactured?
How A Printed Circuit Board is made from PCB Universe
To make a custom PCB, first the electronic diagram of the required circuit is prepared using Computer Aided Design (CAD) software. After that the PCB prototype is developed using Computer Aided Manufacturing Software technology.

The common materials used for manufacturing PCBs are: FR4, FR4 High Temperature, Polyimide, GeTek, Rogers, Arlon, Nelco, Alumina, Ceramic, Bakelite, FR1, CEM1, and CEM5. The size and thickness of the board depends upon the requirements of the circuit. The substrate is coated with a layer of copper. Then, using photosensitive coating, the circuit diagram is printed on the board. The undesired copper is etched out from the board to form copper “tracks”, called traces. This process is known as Photoengraving. There are two other common methods used for developing connecting traces. PCB milling is a mechanical system where undesired copper is removed with CNC machines. Another process is Silk-Screen printing, where special ink that is etch-resistant is used to cover the areas where the copper traces have to be made.

Once the board is ready with copper traces, holes are drilled into the board to assemble leaded electrical and electronic components. For drilling, special Tungsten Carbide drill bits or laser is used. The holes made are filled with hollow rivets or coated through using an electroplating process, thus forming an electrical connection among the various layers. The next step is coating of the entire board, except holes and pads, with masking material. Materials commonly used for this purpose are: lead solder, lead free solder, OSP (Entek), deep/hard gold (electrolytic nickel gold), immersion gold (electroless nickel gold – ENIG), wire bondable gold (99.99% pure gold), immersion silver,

flash gold, immersion tin (white tin), carbon ink, and SN 100CL, an alloy of tin, copper, and nickel. The last step is screen-printing, where the legend and text are printed on the PCB.

Testing Of PCB

Before assembly of components or delivery of Printed Circuit Boards, the board should be tested to find any possible “shorts” and “opens” that could lead to a non-functioning board. A “short” indicates the existence of an undesired connection and an “open” indicates that two points that should have been connected are unconnected. All such errors should be fixed before PCB assembly. It is important to note that not all PCB Manufacturing shops test the boards before shipping; it is sometimes considered an added cost but a vital one to provide a fully functioning board before adding components.

PCB Assembly

Once the board is ready, components are assembled and added to the surface as per the circuit diagram. Some of the common assembly techniques used are surface-mount construction and through-hole construction. Sometimes, a combination of these two techniques is also used for assembly.