Building and maintaining CAD libraries: choose library tools that store component and land pattern data in a generic format that can be used with any CAD tool.

Three driving forces are radically changing CAD library construction. The first is lead-free solder. The next is metric units. And lastly is component manufacturer chaos. This term describes component manufacturers who no longer follow JEDEC packaging standards and are leading the way for new component package development. It seems as though the constraints of standard package data have been thrown out the window, and unique electronic device packages are emerging on the market at the speed of light. These challenges will continue to impact CAD library development and maintenance as we move forward.

Solder

Using lead solder allows the CAD designer to create land patterns that accommodate a variety of alternate component packages, even when they have slightly different component lead dimensions. The land pattern pads can have various toe, heel and side fillets; the lead solder will compensate for the inaccuracy up to a certain point. However, when using lead-free solder, the land pattern size and pad spacing should be as accurate as possible. Only a good land pattern calculator or a good mathematician can determine the best solder joint goals for each unique component.

Due to the non-wetting (no-flow) characteristic of lead-free solder, J-Lead and Gull Wing component leads are not recommended. Component manufacturers are producing new lead forms that are more compatible with the lead-flee solder process. These new component leads are referred to as "no-lead" packages and come in a variety of package styles.

As seen in FIGURES 1, 2, 3, 4, 5, and 6, all of these new component families have flat leads.

[FIGURE 1 OMITTED]

[FIGURE 2 OMITTED]

[FIGURE 3 OMITTED]

[FIGURE 4 OMITTED]

[FIGURE 5 OMITTED]

[FIGURE 6 OMITTED]

The flat no-lead land pattern does not have the typical toe, heel and side solder joint goal as the popular J-Lead and Gull Wing packages for leaded assembly did. Rather flat nolead requires a "periphery" land area that has the same shape as the component lead, just slightly larger for paste mask disbursement. The profile of the ideal chip component overhang can be seen in FIGURE 7, which is taken from the IPC J-STD-001D assembly acceptability standard for chip components. If the chip component is hanging off of the solder pads by no more than 25% in either direction, it is acceptable.

[FIGURE 7 OMITTED]

But if you have a situation where two chip components with metallization on all four sides are placed too close together, they can short circuit to one another. The "bottom only" type of terminal will never cause this problem, and you can place them close together on your printed circuit layout.

Flat no-lead requires an accurate land pattern with tight tolerances. It is covered 100% with paste mask, while overflow solder runs out to the land pattern pad edge when the PCB passes through the reflow oven.

Metric Units

The EU Council Directive 80/181/EEC requires use of the metric measurement system. Beginning January 1, 2010, the European Union (EU) Council Directive (Metric Directive) (http://ts.nist.gov/WeightsAndMeasures/Metric/forum3.cfm) will allow the use of only metric units, and prohibit the use of any other measurements for most products sold in the EU. This will make the sole use of metric traits obligatory in all aspects of life in the EU.

This will have a profound effect on the electronics industry worldwide. All world standards organizations have already adopted the metric measurement system; that is the only dimensional data provided to iNEMI and component manufacturers. Many of today's component datasheets only provide metric dimensions; Imperial units are starting to slowly fade away. This makes the process of building CAD library parts using Imperial units intolerable. Most companies worldwide have resorted to building all CAD libraries using metric dimensions, but many companies still have not converted to the metric system for PCB layout, which further complicates productivity.

Even though America is the only industrialized nation that has not adopted the metric measurement system, every country in the world uses the Imperial measurement system for PCB layout. This is because of several factors, including:

* Component dimensions in the 1980s were predominately Imperial units.

* CAD vendor default values are in Imperial units.

* PCB manufacturers prefer Imperial units because that's what material manufacturers use.

* Assembly shops don't care one way or the other, hut refer to component package data in Imperial units, such as a capacitor or resistor package 1206 = 0.125" x 0.062", when in reality, the package dimensions are 3.2 mmx 1.6 mm = 3216, but the assembly shops do not refer to a 1206 as a 3216.

The eventual goal of all world standards is for CAD librarians and PCB designers to build all their library parts using the metric unit system. This goal will eventually spill over to PCB layout where parts placement and trace routing will be performed using metric units. The only major road block in making the full transition to metric units is that the PCB fabrication material manufacturers (Rogers, Isola, DuPont, Nelco and others) need to convert to metric units. Once this happens, the entire PCB industry will transition because PCB manufacturers will prefer metric-based PCB layouts because it will be easier to work with a single measurement system.

Component Manufacturer Chaos

World standards are taking a big hit in this area, as they cannot keep up with fast-paced component package development for high-speed design and lead-free packaging. Also, corporate greed has crept into the electronics market, setting off global competition for electronic devices.

The reality is simple. It is in the best interest for every component manufacturer to be competitive for survival. This means the current trend is to develop unique component packages that are smaller, cheaper, lead-free, highspeed, low-profile and hermetically sealed. Following existing JEDEC packaging standards is out, and developing unique component packages is in. It is in the best interest for the component manufacturer's stockholders, employees, CEO and CFO to create unique component packages that require a unique CAD library part to eliminate as much competition as possible. Corner the market with their high-speed lead-free component package to generate the highest profit margin.

This phenomenon is taking its toll on CAD librarians trying to keep pace with the increasing number of unique packages. It's also wreaking havoc on world standards, as they are forced to watch while taking a back seat, and have no say about what component manufacturers are producing.

As an end result, the CAD library at every electronics-based company is growing at an unprecedented rate. Unfortunately, many component manufacturers have stopped providing recommended land patterns, and the need for software tools that automatically calculate CAD land pattern technology is rapidly growing. The IPC-7351A land pattern standard is having a difficult time keeping pace with new component package technology, particularly in the land pattern naming convention.

Examples of what component manufacturers are currently doing to make their device packages unique are as follows:

* Two pin devices where Pin 1 and Pin 2 are a different size.

* Making thermal tabs under parts various unique sizes.

* Reverse order pin assignments.

* Randomly deleting or hiding (skip over) pins.

* Inventing new component lead forms.

* Introducing unique pin pitch packages.

* Bending and trimming component leads at various lengths and sizes.

* Component lead tolerances vary from one manufacturer to another.

Each of these items requires the creation of unique CAD library parts. This is also the reason why trying to create world standards is difficult. There is no end in sight to what component manufacturers are going to introduce next. For example, Intel Corp. could introduce its latest CPU processor with a complex high pin count BGA with pins placed on a staggered and random grid that no standard committee would ever approve. Further, the new complex high pin count BGA CAD library parts would take two to three hours to manually build. The industry estimates that PCB designers and CAD librarians spend more than two million man-hours of duplicated effort every year building the same exact CAD library part. That's equivalent to 1,000 full-time jobs of duplication, and this is probably underestimated.

Anyone who now aspires to build a massive CAD library for the purpose of eliminating duplication is chasing a dream. With so many new component families being introduced and innovative electronic devices being invented, as soon as you think you are done, half of what you produced is obsolete. The fact is hundreds of new component packages are introduced every week, so it is a never-ending task.

The concept for companies that sell canned libraries to the public is changing. One approach is to offer a service that will build parts on-demand. In another approach, a software company will offer an average starter library and software tools like the IPC-7351A LP Calculator and CAD interface that automate CAD library construction. The reality of purchasing a CAD library that contains 50,000 parts is that the customer will only actually use 500 to 1,000 of those parts and never use the other 49,000 parts purchased. Also, the customer will still create a unique 20% to 30% of the CAD library parts needed because many parts did not come with the purchased CAD library.

Purchasing software tools that automate CAD library construction is the best alternative to quickly building accurate parts. The tool should also store the component and land pattern data into a file that can be used for historical library documentation. This file should contain everything needed to regenerate a CAD library in any CAD format that you wish to use. This eliminates duplication of effort when changing CAD tools. The library documentation should be customized to only parts used. Your library documentation should be generic and should never change or be recreated if you change CAD tools.

Building and managing CAD libraries is not getting easier, but free products are available that will help you.

TOM HAUSHERR is CEO & director of technology, PCB Libraries Inc. He can be reached at [e-mail].