Ten-Layer High Density Interconnect Board from Rush PCB Inc.

Written by Admin on . Posted in PCB, PCB Assembly and component, PCB Manufacturing

The advent of revolutionary new products, driven by miniaturization of components and semiconductor packages supporting advanced features, is driving the Printed Circuit Board (PCB) industry to increase the functionality of their boards within the same or reduced areas. This includes products such as the hand-held touch-screen computers, 4G network communications, and industrial and military applications such as smart ammunitions and avionics. Eminent PCB manufacturers such as Rush PCB Inc. are providing solutions for the above with High Density Interconnect (HDI) boards.

HDI PCBs use high performance thin materials as prepregs, have fine copper lines, and use the Every Layer Interconnect (ELIC) technology to offer very thin flexible PCBs with very high functional density per unit area. Advanced HDI PCBs make use of multiple layers of copper filled stacked in-pad micro-vias that enable interconnections with even greater complexity.

Rush PCB Inc. is currently building a 10-layer board with an FR4 grade prepreg (TUC-872SLKSP), starting with all layers of 1/3 oz. copper. The outermost layers of copper will be coated with Electroless Nickel Immersion Gold (ENIG), and covered with a coverlay (green mask) of thickness 0.0249” ± 0.003”. Component placement will be aided by a printed white silk screen, while the width and spacing of copper traces in each layer has been carefully calculated to give precise control on the impedance. The board has an overall size of 6.857” x 5.287” and its model number is 104-032-01 Rev 10. Rush PCB Inc. will be manufacturing 100 Numbers of this HDI PCB with a lead-time of 9 days.

Stack-Up Design

Before finalizing the design of multi-layer PCB circuit boards, designers need to confirm the structure of the circuit board primarily based on the scale, physical size, and the requirements of electromagnetic compatibility (EMC). Considering the above, designers at Rush PCB Inc. have decided to use 10 layers of circuit boards. This also decided the placement of the inner layer and the manner of distribution of different signals in these layers—the stack-up design of the multi-layer PCB. This careful planning and rational selection of the stack-up design beforehand will be saving the user a huge effort in wiring and production later.

Two major factors need to be decided once the designers have determined the number of circuit board layers. These are the distribution of the special signal layers and the distribution of the power and ground layers. However, with multi-layer circuit boards such as the 104-032-01 Rev 10, designers at Rush PCB Inc. followed some general principles to obtain the best combination of signal, ground, and power layers:

  1. The signal layer was kept next to an internal power or ground layer, shielded by the copper film of the internal power layer.
  2. To keep a tight control over the impedance, the internal power layer was integrated tightly with the ground layer, so that the thickness of the prepreg between the internal power and ground layers was kept thin, of the order of 2.00 Mils.
  3. To minimize crosstalk, no two signal layers were kept adjacent each other. As far as possible, the designers placed a ground layer in between two signal layers to avoid crosstalk.
  4. To control the ground impedance, designers placed multiple grounded internal power layers.
  5. The layer structure was designed to be symmetrical.

The final stack-up is shown in Fig.1. The overall PCB thickness is only 27.20 Mils or 0.69 mm.

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Every Layer Interconnect Technology

To achieve very high-density interconnection, designers at Rush PCB Inc. have used the Every Layer Interconnect (ELIC) technology. This is a method where each layer has its own copper filled laser-drilled micro-vias. When stacked up, it provides the opportunity for dynamic connections between any two layers in the PCB. Not only does this offer an increased level of flexibility but also maximizes the circuit density. The designers took up the additional complex challenges in routing with Via-In-Pad (VIP) and employing blind and buried vias. Laser drills were used for drilling the via holes, and they were filled up with conductive copper paste.

PCB 104-032-01 Rev 10 uses a total of 32 sets of blind and buried vias between the following layers, as shown in Fig.2:

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Impedance Control

Designers at Rush PCB Inc. have referenced the signals on the top and bottom layer to the ground plane next to them. Likewise, signals on other layers are referenced to ground planes adjacent to them. High-speed signal routing on an inner layer is sandwiched between ground and power planes. Careful design of trace width, spacing, and prepreg thickness has led to a tight control over single-ended and differential impedance as shown by calculations in Fig.3, Fig.4, Fig.5, Fig.6, and Fig.7:

Fig.3

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4

Essential Steps To Know About BGA

Written by Admin on . Posted in PCB, PCB Assembly and component, PCB Manufacturing

bga guide

But although these 3d printed structures are cheap and easy to implement they can lack efficiency. They can be made complex, but for the moment complex 3d printed PCBs are difficult to produce in large volumes. Essential Steps to Know about BGA

When working with PCBs there can be many terms and acronyms that are confusing, and one such term is BGA. BGA, or Ball Grid Array, is a small package on a printed circuit board that is used to mount or hold microprocessors, completing integrated circuits. This article will provide 4 easy steps to get used to and understand BGAs.

Step 1: Benefits of using BGA

There are several different systems in place in order to mount devices in an integrated circuit. One of the earliest is the PGA, or Pin Grid Array, which had many pins to connect the circuit as opposed to pads, which the BGA system has. Although the PGA worked for several years, as technology advanced the pins were more and more compacted together and were not as efficient as BGA, which uses pads that conform to the circuit through solder, which is heated and then melted onto the board. BGA is also efficient when it comes to overheating, as it is able to release heat extremely well preventing the temperature of the circuit rising. This is due to lower thermal resistance of the mounting package. BGAs, because they are so close to the printed circuit board they reside on, have better electrical performance.

Also read: Solder Mask Design Changes Help Prevent BGA Pad Lifting

Step 2: Setbacks of the BGA

As with every piece of technology, there are some unfortunate disadvantages that the BGA has which you must understand if you are working with them. Luckily, the cons are not many, nor will they affect the circuit: it is still your job to prevent any problems as a result of these drawbacks. To begin with, BGAs are less flexible than previous iterations of grid arrays, meaning that bending or breakage may occur in a non-stabilized environment. Similarly, if you have a BGA under extreme conditions, such as extreme heat or extreme pressure, the solder on the BGA can fail to connect the components of the package. If you keep your BGAs in a stable system when manufacturing or working with them, then most of these problems will not affect you.

Step 3: Inspection

BGAs can be hard to inspect for issues when a circuit is no longer working, sometimes requiring X-ray inspection or a CT scanning machine to determine the cause of the problem with the circuit. Due to this, make sure you have the necessary equipment to work on the BGAs, and if you cannot afford to visually scan it, electrical techniques can also be useful, and physically inspecting the BGA is a cheap but dangerous method that can be used as well.

Step 4: Knowing the terminology

Although you are by now familiar with “BGA”, there are multiple other kinds of ball grid arrays that sound but are definitely not similar to BGAs, such as “CABGA”, which stands for Chip Array Ball Grid Array, and “MBGA”, which stands for Micro Ball Grid Array. A full list of variants on the BGA line of equipment can be found online, and we recommend that you check it out to fully familiarize yourself with all types of grid arrays.

Pcb Assembly humidity

Why it is Necessary to Control Humidity in PCB Assemblies

Written by Admin on . Posted in PCB Assembly and component

Pcb Assembly humidity

A Printed circuit board is quite literally an insulated board on which wire is laid to create a circuit. They are a critical and very necessary part of all electronic products. They are in everything from complex computers to basic smartphones. Since they are the base for the circuits that transfer electricity, if they were not included in an average electric machine that machine would just not work not to mention the fact that there would be no place to put the components. The market for PCBs is currently at $60 Billion, that’s Billion with a “B” and growing.
Just like any other electronics, require careful conditions during production to ensure that the integrity of the board is maintained before shipping. In general, things like dust, heat, and the focus of this article, humidity, will have an effect on the PCB.

Also Read: Printed Circuit Board (PCB) Assembly
Just like dust can interfere with and even interrupt circuits, and heat can cause some metal within the circuits to melt, humidity, meaning the amount of moisture in the air, can allow current to run through unwanted areas of the circuit board, causing extreme damage to the board and the circuits on it. Although that should be enough to prove that control over humidity, there are additional factors that could be hazardous to the board, and, by extension, the equipment that it is a part of. Imagine if an expensive new desktop computer fell apart, or in a more extreme example, a computer-guided car or airplane failed mid-transit.
Too much moisture in the board can cause numerous problems from delamination to solderability issues. It is a very simple fact that moisture is not good for any electronic component and this is especially true when it comes to PCBs. Reality is that PCBs are extremely absorbent so both the builder and the end user must use extreme caution when avoiding moisture.
If you are an end user in a high humidity state such as Florida it is highly recommended that you pre-bake the boards before you solder them. Yes, the fabricator will have packed them with desiccant packs to keep the moisture down. But even the short time that the boards are exposed to humidity before they are put into the assembly process can be enough for that board to absorb too much moisture.
The most recommended way of keeping your products safe is to keep a humidity level at around %50, or between %40-%60, which will let the PCBs stay dry while not drying out completely or causing static discharge, which can occur below this level of humidity: a normal amount of moisture in the air only will not affect them.
Remember moisture is our enemy. But baking the moisture out the boards prior to the assembly process is the simplest and most cost-effective way to keep your boards safe and dry.