A Sticky Situation

Written by Rush PCB on . Posted in PCB Assembly and component

The surface tension of liquidus solder exerts a considerable pulling force on a component during reflow. This is why, once upon a time, small components could be relied on to self-align on SMT pads during reflow. They still can, of course, providing that all things are equal, such as pad dimensions all around. But if they’re not, you can expect problems.

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Figure 1. Two SMDs have misaligned during reflow due to uneven pad sizes and disproportionate solder liquidus surface tension.

 

In this case, two components had shifted away from their center location on the PCB footprint during reflow (Figure 1). This was due to the fact that a large SMT pad on one side of the components, see photo, was exerting a stronger pulling force on the component than the ordinary-size pads on the opposite side. More surface area means more pulling force, and consequently component misalignment. It doesn’t matter that the placement machine put the part in the right location beforehand.

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Figure 2. Temporary solder mask glue applied to two corners of each component prior to reflow keeps them in place.

 

Mechanical fixturing simply wasn’t a practical solution. Instead, two dots of temporary solder mask glue were applied to the corners on one side of each component, prior to reflow, to hold it in place. The glue acts as a temporary adhesive and prevents the parts from moving during reflow because it is stronger than the pull of the liquidus solder. After reflow, the glue is easily removed, and the SMDs are perfectly centered. Problem solved!

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Figure 3. Post-reflow, the adhesive is easily removed, and the SMDs are perfectly positioned as they should.

By Roy

Are You Looking for quickturn prototype ‪‎PCB‬ manufacturing & assembly of high quality? ‪‎RUSHPCB‬ is one-stop shop for design, fabrication & assembly of ‪‎PCBs‬. www.rushpcb.com Call: 1 408 496 6013 Email: sales@rushpcb.com

Coming Up Short

Written by Rush PCB on . Posted in PCB Assembly and component

In another PCB assembly challenge, the customer’s BoM called for a through-hole header part to be installed on a circuit board, a mixed technology (SMT and PTH) assembly. A problem became immediately apparent with the first PCB that our operators began to assemble; this was a very thick circuit board (12.15mm thick), but the part specified and received did not have terminal pins long enough to protrude all the way through the PCB to other side (bottom side) (Figure 1). Obviously, we needed the pins to penetrate all the way to the bottom side and protrude so that they could be properly soldered using wave or selective soldering techniques.

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Figure 1. Original part’s through-hole pins are not long enough to go through the board and be soldered from the bottom side.

 

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Figure 2. Cross-section of PCB showing penetration depth of part’s original pins.

What to do?

In this instance, a replacement part with pins of sufficient length simply wasn’t available. The easiest solution (although labor-intensive) required manual removal of all the original pins from the part, and their replacement with longer pins of sufficient length, actually, to form good and robust solder joints on the bottom side of the PCB assembly (Figure 3). Once the longer pins were added, it became a simple matter to re-insert the through-hole header part and solder it in place from the bottom. The parts of the pin protruding from the solder joint could then be dealt with the same way as any other soldered through-hole pins.

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Figure 3. Side view showing new pin length (inset: bottom side view).

By Roy.

Are You Looking for quickturn prototype ‪‎PCB‬ manufacturing & assembly of high quality? ‪‎RUSHPCB‬ is one-stop shop for design, fabrication & assembly of ‪‎PCBs‬. www.rushpcb.com Call: 1 408 496 6013 Email: sales@rushpcb.com

Chemical Free PCB Fabrication and Assembly

Written by Rush PCB on . Posted in PCB Assembly and component

Harmful chemicals and the need to eliminate them from the environment is an issue that is becoming increasingly important now. Exposure to these toxins is not only harmful to the workers in the factories, but also to the consumers who buy the products. Companies who manufacture printed circuit boards, or PCB’s are working hard to make sure the chemicals once used are eradicated from the process.

circuit board

Chemical elimination

Because there are so many pollutants in the air these days, it is becoming increasingly necessary to ensure that as many of them as possible be completely done away with in all aspects of manufacturing. This is why PCB companies are doing away with anything that may be considered a hazard to the environment, and finding new ways to produce the boards without sacrificing quality. The United States has issued initiatives that state that for companies to must comply and adhere to in the elimination of lead-based products.

Non-governmental agencies from around the world are pursuing ways to ensure that safety standards be raised that not only include the workers, but the consumer as a whole. Companies are being brought under scrutiny to make sure their manufacturing processes do not include anything that could be considered a hazard in the PCB’s they are fabricating and assembling. Higher standards are being developed that ensure this is happening in every aspect of manufacturing.

Choosing a company that meets regulation standards

It is extremely important that the PCB company you choose meets with and complies with the regulations that have been set up. PCB companies and their suppliers should be using materials of the highest quality, and manufacturing processes that are free of potentially health threatening chemicals. This not only aids in the health of the workers involved, but also keeps the safety risks to the environment at a minimum. Contamination can be widespread and undoubtedly harmful if these regulations are not followed. Before you buy from a supplier of printed circuit boards, investigate the manufacturer where the PCB originated.

Safety and quality benefits

Quality manufacturers of PCB’s maintain standards that go above and beyond what is required by law. Whether they are fabricating and/or assembling a simple design, or a complicated large circuit board, quality standards are met each time. Even producing large quantity orders means that strict regulations are also in place. They offer reviews and information about the free PCB processes they use in manufacturing and this is something that you can obtain in a matter of minutes. If you cannot locate this information, or the company is unwilling to disclose it, be concerned. Turn to a company who shares this information.

Keeping the environment pollutant and chemical free is an important standard to uphold, and PCB manufacturing centers and the companies they supply to have come to expect and rely on the fact that they are doing everything they can to remove potentially hazardous chemicals from the fabrication and assembling of printed circuit boards.