Earlier HDP User Group project work that has been completed and published compared the different types of high frequency test methods used in the industry for measuring Dk and Df at high frequencies. The HDP project test results being reported on in this paper are based upon that earlier work. This paper will mention but not discuss in detail a weight gain testing protocol that has been developed for driving and controlling higher levels of moisture content within a board. This paper does present the important results of evaluating the effect of moisture content on each of the high frequency test methods using a variety of laminate materials. These test methods include the Z-Direction, Trace-Conductor and In-Plane types of high frequency test methods. Both standard and halogen-free laminate materials were evaluated inthe low loss, middle loss, and higher loss ranges. The following four conditions were tested for each laminate material and test method; As-Received, After 30C/85% RH for 168 hours, After 85C/85% RH for 168 hours, Baked-Dry. The measured differences in moisture content were found to contribute up to a 43 percent difference in the measured Df or Loss values, depending upon the high frequency test method used and the laminate material.

As electronic assembly designs have increased in density and component packaging size and lead pitch have decreased in size, this has placed tighter requirements on manufacturing processes. Tolerances there were considered insignificant in the past are now critical to high yield, reliable products.

With the increased rate of technology advancement, industry standards, material limitations and assembly processes have lagged in response to these changes.

This slide show presents solutions to the relevant Power Module question: "What has to be considered within a PCB, if currents with about 50 A and voltages above 500 V should be designed?"  The electrical and thermo-mechanical capabilities are critical constraints.  2D and 3D CAD models can be utilized to predict creepage and clearance gaps.  Thermal imaging can be used to see  thermal management properties of the Power module functioning under operating conditions.  Tests must be run to ensure that the high currents don't create creep, and the insulation reliably prevents shorts. 

The operation and reliability of any electronic assembly is very dependent on the performance, quality and consistency of the bare printed circuit board (PCB). Without good quality bare boards then, however professional the assembly process, whole batches of product will beat risk of failure, as they will have been built on an inherently bad foundation. Often bare board issues are identified much later in the root cause analysis procedure as the assembler will typically focus first on examining and clearing what they (may) have done before looking at the component parts. Therefore, appreciating how bare boards are manufactured, understanding the potential areas for failure and having access to appropriate inspection facilities should allow, in principle, those involved with Goods Received, or at the first step of the assembly process, to identify and minimise bare board issues ahead of their release into assembly manufacture.

Any external bare board problems may be identified simply with optical inspection techniques. However, if the issue lies within the board, then this will not be optically visible. Such issues include plating thickness variation, poor drilling quality, imperfect through-hole formation, micro-via consistence variation, internal track reduction and poor pad and hole alignment. Looking inside the board to check if these issues occur could be achieved by taking micro-sections. However, this is a destructive, time-consuming and expensive process that requires expert interpretation and is limited to analysing very small sample areas. This makes micro-sectioning uneconomic and unrealistic to do, not only for a typically low value component in high volume manufacture such as the bare board, but also if the bare boards are very few in number and of very high price. Therefore, the use of non-destructive techniques is preferred. This is where X-ray inspection facilities, more typically used for analysing assembled boards, can also be used to identify bare board issues. This paper will illustrate and explain how using 2D and 3D X-ray techniques can show many of the problems described above.