Monthly Archives: September 2017

Variables in Lead-Free Reflow for PCBs

Reflow ovens often show degrees of variability from profile to profile. This may depend on the distribution of components on the board, especially those that are slow heating, heat-sensitive, or of high mass. In general, reflow systems cannot generate one single reflow profile producing capable thermal results for all products.

For instance, a large BGA package on the PCB may not allow more than five degrees of variation near the peak of the reflow profile curve. Therefore, even while the BGA joints show good soldering, there is a probability of frying some other smaller components nearby the BGA package.

Variables during reflow can also be the result of several external factors. There may be limited control for some factors, but others could be uncontrollable. For instance, in some cases, the PCB may be non-uniform, its components may have varying thermal characteristics, or the tolerances of the process controller could be the major contributor. Even the exhaust could contribute as an external factor.

Oven loading is another major factor when creating custom reflow profile for a high-layer-count PCB. The reflow oven characteristics depend on the number of PCBs passing through it, as the total mass of the PCBs and their speed through the oven influences the rate of rise of temperature. Usually, the load capacity of the reflow oven is measured in boards per minute, and this value differs when only a single PCB is passing through as against a batch of several PCBs passing through at a time.

Customers often demand demonstrable settings of the custom reflow profile for their boards. It may be necessary to demonstrate that a given setting fulfills the requirements of a thermal profile for the board, without damaging any other component on it. Sometimes there are requirements to create documentation as evidence that a particular assembly is indeed within specifications. One of the advantages of creating custom profile for a board is it brings a total visibility to the lead-free reflow process when handling that board.

Automated Methods for Lead-Free Reflow

A reflow profiler, such as the one made by KIC, is the most popular method assemblers use for profiling groups of boards they assemble. The instrument works equally well when profiling individual boards automatically and continuously. Assemblers also use it for a cluster of boards consisting of two or three categories.

The KIC profiler has a Navigation prediction software accompanying it. This helps to drive the generated profile deeply within the specifications of the board. Typically, actual profiles need to be run on some boards that match the representative profile for that group. The process must be repeated periodically to ensure the settings remain valid. Used along with the Navigation prediction software, the KIC profiler saves much time and effort when creating lead-free reflow characteristics for high-layer-count PCBs.

Conclusion

Lead-free reflow of high-layer-count PCBs need not be a tiresome exercise provided it is possible to set up a custom reflow profile for a group of PCBs with similar thermal characteristics. Using modern thermal profilers makes the job economical and fast.

Storm Glass Lamp: Raspberry Pi Simulates a Storm

Several people have used the versatile single board computer, the Raspberry Pi or RBPi, as many types of educational devices. In fact, the original purpose of conceiving the RBPi was to use it as an educational instrument to further computer programming among children in schools. It has been serving this purpose excellently, and has managed to go even farther. For instance, the RBPi inspired someone to make a weather-simulation lamp for recreating the weather at any place in the world.

The RBPi within the Storm Glass lamp uses the API Weather Underground for accessing current and future predicted weather at any place in the world. At first glance, one may be rather skeptic about the project, especially when the current weather can be gleaned simply by looking out of the window. However, perception soon dawns when explained that the project is actually able to predict weather—observing tomorrow’s weather today. Alternately, it is possible to keep track of the weather in a distant location, say, a prospective holiday destination.

The designer created the cap and base for the lamp by 3-D printing them. The glass sitting in between the two actually belongs to that fancy mineral water bottle readily available in the supermarkets, which people casually overlook and are forever unable to justify buying. The base also holds the RBPi, a microphone, a speaker, and other varied components such as a NeoPixel LED Ring and a Speaker Bonnet from Adafruit.

The Storm Glass lamp uses two important arrangements. One of them is the rain maker and the other the cloud generator. The rain maker uses a tiny centrifugal pump working at 5 VDC to pump water via glass tubing into the lid, from where the rain falls. An ultrasonic diffusor/humidifier, also working at 5 VDC, forms the cloud generator. Only the electronics parts of the diffusor, which create the ultrasonic signal, are necessary, and the rest can be discarded. All the equipment goes in together into one spectacular lamp.

By installing Alexa Voice Service within the Storm Glass lamp, and setting it up to use the Weather Underground API to receive data related to weather conditions in a specified place, these conditions are easily recreated within the lamp, functioning as a home automation device.

When taken outdoors, and placed on a nightstand, the Storm Glass can actually recreated he weather conditions outside. It gives a weather forecast for the day by checking the weather periodically online. For instance, if the prediction for the day is rainy, expect some rain to fall within the Storm Glass Lamp. If the predicted says partly cloudy, you will see clouds forming inside, with some sunshine interspersed.

An RBPiZW powers the project, as it needs both Wi-Fi and Bluetooth support. Apart from the Speaker Bonnet, mini water pump, and the ultrasonic diffuser, there is a NeoPixel 12-LED ring, a 2.5 A micro USB power supply, 8 GB micro SD Card, two TIP 120 transistors and two 2K2 resistors. Additionally, you will also need tubing for moving water, lots of hot glue, and the 3-D printed parts to hold all the above together. All the parts operate at 5 VDC, so there is no additional converter, and the RBPIZW controls everything.

Lead-Free Reflow for High-Layer-Count PCBs

High-layer-count multilayer printed circuit boards (PCBs) present one of the most difficult cases for adaptation to the lead-free reflow assembly process. Often, these boards have through-hole and hand-soldered components, along with the requirement for two or more rework cycles. The slower wetting and higher reflow temperatures of lead-free solders place an enormous strain on the laminates and copper-plated hole barrels of the vias, with resulting loss of reliability.

Restrictions on Hazardous Substances

Printed circuits are coming under increasing requirements from environmental regulations. Waste Electrical and Electronic Equipment (WEE) directives and the European Union’s Restriction of Hazardous Substances (RoHS) are significantly affecting the requirements on the base materials used for manufacturing PCBs.

The most popular solder material so far consisted of the tin/lead (Sn/Pb) alloy. used for the assembly of PCBs for many years. The melting point of eutectic tin/lead alloy is 180°C and during assembly, reflow temperatures commonly reach peaks of 230°C. However, one of the major restrictions RoHS places is in the use of the element lead (Pb). This has resulted in development of alternatives to the tin/lead alloy, which are now replaced typically with the SAC alloy, whose primary ingredients are tin/silver/copper (Sn/Ag/Cu).

The SAC alloy has a melting point of 217°C, with reflow temperatures typically peaking around 255-260°C. This rise in the assembly temperature, coupled with the possible requirement of multiple exposures to these temperatures means the base material must possess improved thermal stability. Although there are several effects of lead-free assembly temperature on base materials, three effects deserve special attention for improving the thermal performance. These are:

* Glass transition temperature
* Coefficients of thermal expansion
* Decomposition temperature
*
How Higher Temperature Affects Laminates

The traditional Sn/Pb assembly process exposed the PCB to peak temperatures of 210-245°C, with 230°C being a very common value. At these levels, most lamination materials do not exhibit significant levels of decomposition.

However, at temperature ranges of 255-260°C where the lead-free assembly process operates, traditional lamination materials exhibit a 2-3% weight loss. Furthermore, multiple exposures to these temperatures may result in severe levels of degradation. Thicker boards, many of which are 20+ layers, aggravate the situation, as many of the layers are power or ground planes.

Although one of the simplest ways of complying with the RoHS directive of lead-free assembly may be to change the base laminate and replace the tin-lead solder, this does not work out satisfactorily for thick, complex, high-layer-count PCBs.

Creating Custom Reflow Profiles

Creating custom profiles for high-layer-count PCBs works well for the lead-free reflow assembly process. If the new PCB has thermal requirements close to that of some other PCB already being assembled, tweaking the settings for the existing PCB may be adequate. However, for a new PCB whose thermal requirements do not match any existing types, there may be thermal challenges. In such cases, developing a new profile may be more cost-effective ultimately.

Conclusion

Redesigning to reduce the thickness and the number of layers of high-layer-count PCBs is the way out in achieving reliable lead-free reflow soldering. Moving over to HDI technology, together with the use of BGA connectors, offers a viable solution.

How Counterfeit Electronic Parts and Components Affect Businesses

Although counterfeiting has been an age-old industry, it is only recently that the impact of counterfeit electronic parts and components has come to be highlighted. The public is slowly gaining the awareness of the implications and risks such counterfeited electronics bring to trusting users.

It is difficult for manufacturers to trace the origin of the counterfeited parts compared to the traceability present for the authentic components. It is possible these are older, but legitimate versions of the part, and someone has reprocessed them. On the other hand, these are legitimate fakes, which someone is trying to pass off as real. In both cases, their quality is highly suspect. Receiving counterfeit electronic parts or components in your business can result in mechanical and electrical defects, leading to financial risks and finally to loss of reputation and goodwill.

Mechanical Failures

Scrupulous elements recover a huge number of electronic components and parts from e-waste and reprocess them to sell as new. However, the stress of reprocessing these parts, especially integrated circuits, makes them susceptible to damage. As reprocessing elements do not usually follow proper manufacturing processes, they compromise the integrity of the components, and they occasionally fail to meet the stringent environmental requirements in the field.

Electrical Failures

While reprocessing, usually there is little or no effort to protect the component from ESD damage. Although the counterfeit component may be functioning in the circuit, it is difficult to predict when they will fail. The typical design of genuine electronic components allows them to function for a certain amount of time under specified conditions of use. Reprocessed parts generally fail as their useful life has been exceeded or they have endured dubious production controls and improper processing before they were resold as new.

Financial Risks

Counterfeit electronic components malfunctioning in the product or failing within the warranty period may lead to huge financial ramifications for the business. The financial risks may not be restricted only to simple replacements of the product, but may involve insurance compensations in case human lives are endangered, as could happen in premature failure of sensitive medical devices. The short-term savings from using counterfeit components may not be worth it, considering the financial backlash may turn out to be too huge for the business to handle.

Loss of Reputation and Goodwill

It takes a lot of effort to build up credibility, reputation, and goodwill in business, and these are essential for sustenance and growth of the business. However, the above can only happen provided the customers perceive the products to be of the quality and reliability the business claims they are. Counterfeit electronic components and parts leading to mechanical or electrical malfunctions and failures can easily undermine customer confidence in the business, leading not only to financial loss and legal hurdles, but also to loss of reputation and goodwill.

Conclusion

For safeguarding the business, its customers, its reputation, and goodwill, it is necessary for a business to take proper steps to prevent any incoming counterfeit parts and components.