Economics in PCB Design: cost and value

Today, let's talk about the economics of PCB design. In the process of PCB design or system design, every decision needs to be considered from design, manufacturing, quality, time, cost and other factors. Some of these factors are visible, while others are not. However, if at each decision-making point, a comprehensive consideration is made from the perspective of engineering and cost at the same time, it is most likely to find a balance and design products that meet the functional requirements and have reasonable cost. The price (cost) and value of everything are obviously not the same concept. Every successful PCB product must achieve the best balance between design requirements and product cost.

When we choose PCB assembly manufacturer, whether it is PCB factory or PCB assembly factory, we often make a mistake: choose the lowest price. The cost of PCB design includes not only the manufacture of bare board and the assembly of devices, but also the cost of rework, maintenance, scrap, alternative materials, on-site support services, etc. The cheapest PCB is likely to be scrapped in the final assembly process due to quality problems. Let's discuss which factors will affect the cost of PCB, and make the best balance between cost and value.

 

Basic elements

When selecting PCB, the following basic elements need to be considered first:

Obviously, the more layers, the more cost of design and manufacture. Generally, two to three layers are enough for RF and microwave design; more than two layers are needed for high-speed digital system or more complex design. However, the actual situation is that the number of layers of PCB designed is more than the actual number of layers needed, which is usually caused by unreasonable layout and wiring, and unreasonable distribution of power supply and ground plane; but sometimes, it is deliberately: some IC original factory issued public design (reference Design), in order to ensure the reliability of design and timeliness of release, additional ground plane or power plane will be added, which not only reduces the difficulty of layout, but also reduces the risk of signal integrity. You will recall that experienced ODM or design house can often reduce the board layer to achieve the purpose of cost down without affecting the product function?

However, from the perspective of design and production, the ultimate goal must be to find the best balance point: that is to achieve the functional requirements with the smallest board layer, and meet the safety certification. Of course, "time" is also one of the considerations. If a product needs TTM (time to market), it cannot achieve the lowest cost. That's why new releases are often more expensive, and then, over time, cheaper. It is not only the reason of "mass production", but also the design optimization (such as reducing the plate layer).

 

Selection of laminate

The key to the selection of laminates is to match the needs of the products. The key properties of laminates include TG (glass transition temperature), ER (dielectric constant), etc. The choice of base material is also sometimes dependent on price factors.

 

Avoid "special" substrates

At present, the most commonly used PCB substrate on the market is FR4 glass fiber board. If CEM's half glass board or even paper board is selected for price reasons, Congratulations, not only the quality of PCB will be in a mess, but also the product development cycle will be prolonged due to supply chain problems (out of stock). If the board factory is not reliable, it will also use various excuses to let you order more base materials. Back to calculate, the price is not much cheaper.

 

When choosing the materials commonly used by the board factory, make sure that the board factory has rich experience in using the materials you choose, because this can ensure the accuracy of the chemical treatment of the materials in the process of bare board production. Even if there are small differences, the board factory knows how to deal with them.

 

In addition, when choosing laminates, the board manufacturer should be the same supplier. In case of multiple suppliers, the key attribute parameters must be the same, because the small differences in the production of laminates will also affect the overall quality of PCB. For example, fiberglass cloth is one of the three main components of laminates. The heat in the lamination process makes it shrink, while the degree of shrinkage of laminates from different suppliers is different. When PCB board manufacturer use different laminates in the process of PCB production, it is likely to cause PCB bending due to different shrinkage of fiberglass cloth. The bent PCB must be scrap. Even if the board factory admits that it is their problem, it will affect the overall production progress. For TTM products, this is undoubtedly fatal.