Prototyping Section

Success Factors for a Robust Product

Three major factors that will contribute if your RF Module Design will be successful will be briefly discussed: design, assembly and last be not least the cost.

1. Design

Integrated RF components

Integration of RF components into the module carrier can give the custom RF module solution a major design advantage and not to mention a cost advantage in comparison to standard available components. The integrated RF components can be tailor made for the application so that the matching and filtering are optimum. When planning the layout and the build up of the module carrier; try to keep the area space between the physical components and the areas size of the integrated RF components the same size. This is assuming that the integrated components are buried underneath the physical components. The build up of the module carrier will be dominated by the RF filter characteristics and the complexity of routing. Similarly, the choice of balun that shall be used will also be a trade of between size available and performance. Apart from filters and baluns, it is quite common to integrate matching networks and switches into the module carrier. When the RF module is very compact then each integrated RF component should not disturb other sections of the design.

Compact RF Design

The design rules for standard application boards are typically run of the mill. Advanced designed rules can not be used since the cost of the application board would dramatically increase. RF modules are normally very small in comparison to the application boards in which they are being used so more advanced design rules can be used without a great impact on the price. By using more advanced design rules on the relatively small RF modules; usually impacts a relaxation of the design rules required on the application board. Since the price of LTCC is expensive it is crucial to keep the design as compact as possible. Integration of RF components are normally positioned around routing of non-sensitive signals and vias. This reduces the size even more, than just integrating the RF components into the carrier substrate.

Technology

Choosing which technology shall be used for the design is not always so straight forward. It is vital to consider the whole application when choosing the technology. The technologies which have been traditionally available for RF module design have been LTCC, FR4, Rogers & thick film). Each technology has its advantages and disadvantages. It can not be stated that one of these technologies is better than the other in general terms. What is becoming more popular in very compact designs is using a newer technology such as SIP. Even with newer technologies such as SIP; the whole application has to be taken into account before deciding on which technology should be used for your application. Which technology shall be used is also linked to the cost 'v' size 'v' performance balance.

2. Manufacturing

Producing a design that works in the lab is not good enough to prove that the concept will go the whole way to high volume production. For the design to be successful, it must have a low manufacturing price, high production yield and high quality reliability. Producing a design that does not have all these three important manufacturing factors simply means an unsuccessful design. There will be yield loss and the expected yield must be estimated correctly. 100% yield exists only in the power point world. Designing a product for very high volume amplifies the importance of yield; since profit margins on high volume products are limited, a drop in the yield can easily make any product into a financial drawback.

When the manufacturing has started, it is important to start to think about increasing the yield and quality. An important factor for designs that are susceptible in yield fluctuations is to be able to quickly locate the problem that is causing the yield loss. Usually, the yield for the first few production batches is a lot lower than the expected target yield goal. The difference between module design and IC design is that a lot of the work is still left when the module production starts.

3. Cost

By integrating RF components into the module carrier then the carrier cost will pay for itself since external components can be removed. Yield loss on the application board level is a main reason why many companies are starting to use pre-tested modular solutions that ensure greater yields. However, if there are no yield loss issues on the application board then the purpose of using a modular solution can be questioned. There are other factors why a modular solution can be used apart from yield improvement. If the modular solution only contains RF parts; then the RF module can be type-approved (FCC, ETSI etc.) and pre-qualified towards a radio standard such as Bluetooth. The advantage for the final application board would then be re-using of the RF module's type approval and pre-qualification.