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When selecting PCB technology for your board, you should know the PCB factory have different lamination options to meet your required PCB technology of your board. The used lamination method is based upon your required board type and additionally upon the type of PCB-technology that you want to apply to the board during the PCB process. This article will give you a quick insight into the different lamination options at your disposal.
The PCB Lamination process
Before understanding the lamination process in a PCB factory, you must first understand the materials from which you can build your lamination. A PCB typically contains different components, such as copper layers, prepreg(resin/glass fiber) and innerlayers. These are key-components and can be delivered in many thicknesses and material variations.
This is what an Innerlayer looks like:
An innerlayer is typically pre-laminated by the material supplier, who will deliver this to the PCB factory in various thicknesses, sizes and types. The material supplier laminates 2 horizontal copper sheets together by separating them with a dielectric. Here are some thickness examples: 0.1 mm, 0.2 mm, 0.3 mm, 0.51 mm, 0.76mm, 1.0 mm, 1.2 mm and 1.55 mm.
The dielectric in such 2-sided lamination (inner layer) contains typically Resin(glue) and weaved Glass fiber. This laminated inner layer can become an outer layer, if it is processed as a double side PCB, where it will become etched, drilled and plated. The dielectric and the copper sheets used in the innerlayer, can also be supplied directly to the PCB factory as individual sheets, which can be used for customized lamination, when making a multilayer board.
This is what a copper sheet looks like:
Thicknesses are typically 18 µm, 35 µm, 70 µm, 105 µm etc.
This is what a Prepreg sheet looks like:
The thicknesses and their characteristics are many, but here are some of the most common types: 106=0.05 mm, 1067= 0.066 mm, 1080=0.075 mm, 2113=0.1066 mm, 2116=0.12 mm, 7628=0.19 mm.
Prepreg sheets are layers of glue and is a typically a combination of Glass fiber weave and a resin. Prepregs varies in many thicknesses and type of weave. Prepreg sheets are used in the lamination process to glue Inner layers together or to glue individual sheets of copper and an inner layer together.
The material supplier can also supply a laminated dielectric, with only one sheet of copper. This is known as a single sided lamination and this is what it looks like:
If you require more than 2 layers of copper on your PCB, the PCB supplier will use all the above-mentioned sheet types as components to build a multilayer PCB.
A 4-layer PCB, is laminated by the PCB factory using 2 innerlayers, which are separated by one or multiple prepreg. Adding multiple prepregs, will help you meet the overall thickness. This is the most commonly used 4-layer PCB and is also the less expensive option as each innerlayer will be etched and processed simultaneously before it is laminated. This type is usually not relevant for HDI.
The alternative 4-layer PCB is in fact HDI friendly, but also more expensive, as the PCB factory must use more components and more time for processing. It can be laminated using individual copper sheets for top and bottom layers, with an innerlayer in the middle. The innerlayer and the top and bottom copper sheets are separated by prepreg. First the innerlayer will be processed(etched) and then it will be laminated. After lamination the top and bottom copper sheets will become etched.
Building even higher number of layers will require the factory to apply additional innerlayers or prepregs and copper sheets to above 4 layers examples. If considering HDI, sequential lamination can be required. For sequential lamination, the board will go through at least two lamination processes, but depending on the interconnection of via’s between layers, it might need to go through additional lamination processes. Sequential lamination has generally been driven by the computer chips packaging, mobile phone, medical products and satellite industry, where the customer use small BGA packages is high and for which the thin and tight fanout is required.
Designing a PCB, selecting the use of technology and design rules for optimized and cheapest manufacturing, require extensive know-how about the limitations of the used technology. Keep in mind that there is often more than one technology that will meet your demand, but understanding the best alternative usually takes years to master. Should you require guidance, seek for people with expertise in the field and they will help you navigate through the jungle of PCB technology selections, that will serve your demand best.
PCB Layout Guide
PCB Layout Guide
Designing your board is very important and exiting stage in the PCB development. There are many limitations and requirements that need you need to remember when designing it. Making a mistake in the design phase will cause starting all over again and result in starting another production if it is not caugt in the design phase. This article will take you through the basic of PCB Layout and guide you through the important steps to remember. At the end of the article we have summed up of the most common mistake done by PCB designers, in order to avoid you making them in your board.
What does the PCB Layout files contain?
The final PCB Layout files should be your Gerber files. The Gerber files is a 2D vector image that has been the industry standard for PCB fabrication data for a long time. The Gerber files describe how the board looks, the location of the holes, vias, lines, copper, silkscreen, outline etc. The Gerber files contains each image file for each individual filetype, additional layer will also have their individual files. A simple way to understand what Gerber files is, to see the Gerber files as the recipes for the manufacture to make the board.
What should you consider when designing your board?
When you need to have your board designed and be ready for production you must clarify the need and functionality of the board. In order to get an overview of your board and its functions it is recommended to make a schematic of your design. With this schematic it will be easier to understand the design and be a guide for the traces and where component should be placed. It can also be used to explain for the designer your needs or it can be used as a check-up of the finished design. Furthermore, it is always good to have a reference and overview of the idea.
When designing the board, you need to know the limitation as size, thickness, shape and its capabilities. What capabilities should the board have, should it have Bluetooth, Wi-Fi, NFC, etc. These capabilities will have impact in the way you are designing your board, because each technology is requiring special design rules. Therefore, it is important to understand the design rules of the technology that are applied to the board when designing it.
If you are an experienced PCB designer you can make the design yourself. Another option is that you can outsource it to an experienced designer, depending on your skills, the designer might route your board more efficacy, which is good if you have real estate or design rule issues.
- Manufacture specification:
- When you are routing your board, it is good to know your manufactures specification on trace spacing, number of layers, trace widths etc. If you design your board, and the manufacture can’t produce your board you might end up reroute your board design or find new manufacture.
- Avoid using multiple hole size:
- When designing your board, we recommend not to use too many different holes size. Different holes in your design will result in that the manufacture have to use different drills. This will in the end make your board more expensive.
- Make sure your material is on stock:
- Make sure if you design a complex board that required material is on stock. If you are using a unique material that is not on stock at your manufacture, you must add up extra lead time in your planning. Some material can add up surprisingly a lot of days extra.
- Always make a DFM Analyse:
- Making a DFM analyse is always something we recommend our customers, if there any mistake in your design, for example that could short circuits your board, is good to know before your board has been produced.
- Back up:
- Always back up your latest design. There is nothing worse than redo your work from beginning because you did not have a backup. With all the cloud option that’s available today, it is the worst thing that can happen to your work and add unnecessary extra time for getting your finished board.
- Doing holiday season, the manufactures will be busy, have in mind if there are any upcoming holidays in your manufacturing country to avoid extra lead time. In some cases, the holiday might have a huge impact in other countries, this will add extra days to manufacture, simply because the huge increase in demand.
Creating your Layout files for the first time, can be time consuming and result in that you have to redesign the board a couple of time, but in the long run it will help you to create better boards. There are plenty of help to get from experts, that only work to help with PCB layout. Seeking help for the couple of first projects is normal and will help you get a better understanding of the PCB Layout universe.