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How to design HDI PCB?

petter / 2021-01-01

Contents [hide]

Accompany the consumer electronic products developing, people are pursuing for more small and clever products for easy carrying.This cause the engineer must use more small PCB size to finish the product design, so Multi layer HDI PCB board will be a trend for future 


PCB industry. For engineers,must know some design rules of HDI PCB and production capacity from different PCB factory, here I suggested PCBA STORE for you easy and quick to get HDI board cost. 




Why HDI PCB Design is Important


Compact design


The high-density essence of the HDI PCB implies that the board technically takes minute physical space. Mainly, a combination of design features such as buried vias and blind vias, and microvias makes it easy for this design to have a solid build. With solid design, these circuit boards are more multifaceted.


Lightweight


Customized PCBs employ broad types of materials, but in most cases, they encompass a combination of fiberglass, copper, aluminum, and others that are heavy. The good thing about HDI PCBs utilize cooler and lighter materials, fulfilling several designer requirements and fostering better performance and functionality. With HDI PCBs, it is easier to embed many electronic elements on a small board.


Exceptionally versatile


One remarkable thing about HDI boards is that they are an appropriate option for space, performance, weight, and reliability.


Phenomenal signal integrity


One fantastic thing about HDI PCB boards is that they employ blind and via-in-pad through a technology. This concept is ideal in setting the components as close to each other as possible, hence cutting down or reducing the signal path length. HDI PCB technology detaches Via end and thus minimizes signal reflections and boost the overall signal quality.


Economical


With HDI PCBs, it is possible to ensure that each penny is invested the right way. HDI PCBs help boost the performance by ensuring that every component is preserved to the maximum. It employs all the element s in one board instead of using many standard PCB boards.



Reliability


Employing stacked vias ensures that HDI PCB designs are super protected against acute environmental conditions. Ideally, microvias possess outstanding reliability compared to their typical counterparts because they utilize the minute aspect ratio.


Challenges for HDI PCB design


There are many challenges for HDI PCB design, including the following four aspects.


1. The cost of the board


PCB Cost is one of the major challenges influencing HDI PCB design, where most of the cost is used in manufacturing processes like drilling, lamination, and plating. There are up to 5 cycles for the lamination process, which is hard on materials and joints. The fact that HDI costs more, it allows more routing, employs less routing layers, and less board material required for the array.


2. Creating the uVia structures


There are many steps involved in developing uVia structures. There are microvia pads, variable depth blind vias, staggered vias, and stacked vias, and all are technical to build. In the case of variable depth blind vias, it might connect at one layer or more; however, it will require antipad if not linked to a layer. Variable depth blind vias also employ a larger hold size and pad compared to conventional counterparts. They also require extra cost. For stacked vias, the components require technical registration and often have more possibility of failure.


3. Fabrication Issues


HDI manufacturing encompasses a different process that uses a high aspect ratio, thus driving down or reducing overall yield and increasing the cost. Also, traces usually are 4/4 or 3/3, but it is recommended to utilize extra spacing.


4. Plating Process


The plating process is the primary issue. To ensure the right hold plating integrity, the aspect ratio must be confined to 1: 0.8 for blind vias. For the advanced value board, the aspect ratio has to be maintained at 1:1. Because of this aspect ratio confinement, the HDI PCB manufacturer must choose a unique pre-preg like very thin, with an ideal response to laser drilling.


Basic HDI Design Guidelines


Anytime you are dealing with light-pitch BGA and the vias and traces that link to it, then there are basic design guidelines that follow:


1. Remember To Check The Capability Of The Manufacturer


This is a must prior to planning a new PCB design, however it is a more important aspect when it comes to HDI design. You should remember that manufacturers have a distinct capability. Therefore, it is vital to check with your ideal manufacturer before developing an HDI layout that is not easily fabricated.


2. Consider Tracking The Spacing Between Pads And Traces


A similar concept applies in BGA with 1mm pitch, and the sole aspect that changes is mounting to microvia sizes. The clearance values of solder masks are primarily of similar size with trace width. This depends on the pad pitch and size of the pad.


3. Avoid Using ELIC Or Staggered Vias If You Don't Require Them


The concept of HDI routing is to offer enough space for routing on both the inner layer and the surface. Although it can be alluring to stake the whole span of the product, do not utilize the additional space until it is worth it.


4. Consider Fewer Layers


Several layer count board introduces a high manufacturing cost and many PCB assembly steps. If you consider fewer layers, then you can notably customize the cost per every board.


5. Remember Signal Integrity When Dealing With HDI Boards


Any HDI set-up has to be tailored with a high-speed layout in mind. In case you are dealing with an RF board, you can consider high-frequency guidelines. This principle applies to the PCBs as well as in HDI PCBs when scaling. If the HDI board you are using needs impedance managed routing, you would require to strictly design stackup and traces to guarantee a compatible impedance with signaling quality.


The Keys to Successful HDI PCB Design


One of the main aspects that differentiate HDI PCB boards from ordinary boards is that HDI has higher pad density and wiring. They yet possess smaller trace spaces and widths. This is easily achieved by employing technology like buried vias, blind vias, and micro vias. This technology also makes them a bit expensive than their counterparts. Usually, three key aspects lead to successful HDI PCB design.


The first aspect is that unlike the customary types of boards where there are TH (through holes) vias, HDI employs microvias, which help boost the density of routing on the inner layers.


The second aspect is that you will need to ponder a unique stackup layer technique, which will help you get rid of the through-hole vias.


The third aspect is that you have to make sure that the microvias are positioned in a way that develops boulevards and channels to boost routing.


The Best Material for HDI PCB Design


Signal energy loss determination at high frequency needs HDI PCB materials with low dissipation factor or minimal dielectric loss tangent. These materials are categorized into four.


1. Normal Speed And Loss


These are FR-4 family PCB materials. Their frequency response vs. dielectric constant is somehow not flat and possesses a dielectric higher loss. Thus, their feasibility is bounded to a few analog/ GHZ digital applications. A good example can be Isola 370HR.


2. Medium Speed And Medium Loss


These are materials with level DK vs. response frequency curve, where Dk loss is approximately half the standard speed materials. They are a kind of materials ideal for ~10GHz. A good example can be Nelco N7000-2 HT.


3. High Speed, Low Loss


These are kinds of materials with low dielectric loss and level DK vs. response frequency curve. They help create minimal undesired electrical noise than many other used materials. An example of such material can be Isola I-speed.


4. Very High Speed, High Signal Integrity, Very Low Loss


These are often materials applied in RF/microwave. They possess minimal dielectric loss and level DK vs. response frequency. They are appropriate for applications of up to ~20GHz. One good example of such materials can be Isola Tachyon 100G.


Basically, materials influence the electrical performance mostly in signal traces. Therefore, you need to consider choosing the right materials.


Design Tips for HDI PCB Manufacturing


The PCB layout is somehow technical that calls for the designers to come up with gritty decisions about the kind of specification to prioritize. The process can also be daunting if the layout is employed in the system industry like medical devices, military, aerospace, automotive, or high-performance machines such as HDI or IoT. Here are the design tips to employ for HDI PCB manufacturing to help you make this less stressful experience.


1. Pick Via Types To Help Reduce Process Entanglement


The option of vias is a vital decision that helps evaluate the manufacturing process and equipment needed. It also influences the cost and processing time. Employing blind, microvias, or buried helps minimize material cost and the number of layers; however, the option of using dogbone, via-in-pad, or near pad vias influences the intricacy of the process.


2. Select A Few Components To Employ HDI


The selection of components is essential for HDI boards. They help evaluate locations, trace widths, sizes, and types for stackup and drill holes. Undoubtedly, performance capacity is a chief contemplation; but traceability, packaging, and availability must also be pondered. Having to redesign the plan or replace components can push up extra material cost and fabrication time.


3. Route Trace To Reduce Signal Integrity Problems


One benefit of HDI is that it can employ a few trace widths for the proliferation of signals. Despite being minimized, the trace width must be tailored towards accomplishing the ideal signal integrity. This encompasses employing consistent path impedances, shortest trace length, and power signal isolation.


4. Pick Stackup To Reduce Material Costs


The choice of PCB stackup also influences HDI PCB manufacturing costs. The number of layers and type of materials impact drilling cycles and lamination needed. When considering these decisions, you should remember that cost is a determinant.


Designing HDI PCB is not that easy, especially to the novice and finding a great expert to handle the task is even more challenging. The good news is that there are reliable HDI PCB manufacturers like PCBA Store with a professional team of engineers who can handle the task for you.


Hope above information will helpful for you to finish the HDI PCB design!


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