Making the Most of Conformal Coatings
with Press-Fit Connectors
Press-Fit Connectors Pierce Conformal Coatings for Added Value
Technical Article
an Amphenol company

The printed circuit board or PCB has been the preferred method of designing electronic
circuits since the 1970s. With the birth of semiconductors and the advent of electronicminiaturization, the established methods of joining circuits, especially using wires and wire
wrap connectors, fell out of use and the PCB has come to dominate the electronics market.
The PCB offers several advantages over previous technologies. It is compact, it can be massproduced in almost any shape to suit the application and, with the development of multi-layer
boards, it has become an extremely complex and capable solution for electronic designers.
When the PCB was first introduced, all the components were mounted to the board using
through-hole pins. These were inserted through holes that were drilled into the board andplated to provide continuity. Once placed into the board, the underside was then soldered toensure secure physical and electrical contact. While through-hole mounting provides a very

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1Making the Most of Conformal Coatings with Press-Fit Connectors

stable solution, the disadvantage of this technique is that components can only be mounted
to the top surface of the board. The typical soldering process uses a wave soldering machinethat would damage any components mounted underneath.
This limitation has been overcome by the advent of surface-mount technology (SMT). Using
SMT, components are fixed to pre-placed solder pads on the surface of the PCB. The
components are then secured to the PCB using heat from a reflow operation, which melts thesolder pads and forms the connection. As the board does not use a traditional wave solder
bath, components can be mounted to both sides.
Through-Hole and Surface Mount
SMT boards also allow a far greater density of components to be placed on the board,and SMT has largely replaced through-hole techniques, especially for micro components.
However, through-hole mounted components continue to provide a reliable way to connect
several layers of a PCB. In contrast, an SMT component that is mounted onto the surfaceof the PCB cannot penetrate the board and provide this same connection. Additionally, SMTcomponents are not capable of the same current carrying capacity as through-hole ones. In
these circumstances, through-hole components are ideal.
There is therefore still the need for through-hole components, especially when providing
the connections from the PCB to the outside world. In addition to solder tail connections,many designers like the flexibility of press-fit connectors, as they can be mounted to a PCB
after it has undergone the soldering process without the need to reheat the board. Press-fit
connectors are not a new concept, and have been used in the electronics industry since theearliest days of PCB design.
Conventional press-fit terminals use solid pins with a square cross-section. The sharp cornersof the pin are designed to deform the plating of the through-holes to form a gas-tight seal,
ensuring both a secure mechanical joint and a reliable electrical connection. The downsideof this technique is that pressing the pin into the hole risks damage to the PCB, and it israrely repairable. Despite this, press-fit connectors offer some key advantages for designers
and manufacturers. As they are mounted after the solder reflow process, they do not require
additional heat to be applied to the PCB. This reduces the danger of damage caused bythermal stress. As the joint is solder free, it removes the risk of failures due to defects in thesoldering process or deterioration over time.

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Making the Most of Conformal Coatings with Press-Fit Connectors

New Press-Fit Technology Facilitates Conformal Coating
Press-fit connectors therefore remain a popular choice for PCBdesigners. To provide a modern solution that will provide the benefitsof press-fit termination without the drawbacks, Positronic has createda solution using contacts with compliant tails. Named “Omega” after
the Greek letter that they resemble, their flexibility ensures the samestable mechanical and electrical joint without the damage to thethrough-hole plating.
The Omega press-fit contact provides further advantages for designers who need to protect
their printed circuit board. The growing sophistication of miniaturized electronics has allowed
PCBs to become more compact and complex. Their small size means they can be usedin devices that are deployed into tough conditions. Away from the shelter of the laboratory,
modern electronic systems are tasked with delivering reliable performance in all kinds ofenvironments. Even PCBs that are sealed inside enclosures must be protected.
One of the common causes of failure in electronic systems is the damage caused byoxidation. Exposed to moisture in the air, the metallic components on the PCB can corrode.
With enough time, this corrosion can cause permanent damage and create short or open
circuits. The resulting failure can produce results that range from inconvenience to lifethreatening.
To protect the PCB against damage caused by moisture, many manufacturers turn toconformal coatings. A conformal coating, often parylene, is a polymer that is applied to thePCB using a vapor deposition process. The parylene is introduced into a chamber as a cloudvapor that covers the entire PCB with a consistent thickness that is resistant to water andother contaminants.
Making the Most of Parylene Coatings
The disadvantage of parylene is that it must be applied after the soldering of components tothe PCB, as the heat of the reflow process would melt the polymer. For most components,
this presents no problem. However, the polymer cannot be allowed to settle on the connector
contacts as it is non-conductive, which would prevent the connector from working asintended.

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Typically in these cases a mask is placed over the mating face of the connector before
the coating is applied. In this way, the contacts are prevented from being exposed to theparylene. Once the coating has been completed, the mask can be removed and the PCB
used as intended. The process of applying and removing the mask is time-consuming as itneeds be conducted by hand, which adds significantly to the overall manufacturing cost ofthe PCB.
The Omega press-fit contact technology offers an alternative to the costly and timeconsuming process of masking. Its innovative design means that a connector that is fittedwith the Omega contact can be mounted to the PCB after the parylene coating has beenapplied. The contact simply pierces through the thin conformal layer, and its Omega-shaped
design ensures a secure, gas-tight joint when fully seated.
Testing and Qualification
Positronic is committed to providing fully tested solutions to customer.
To prove the performance of the Omega contact with conformalcoatings, testing was conducted using Positronic standard density
PCD press-fit connectors with size 20 Omega contacts, as well asproducts with size 22 Omega contacts from the high density PCDD
series. A parylene coating was applied to PCBs prior to the insertionof the press-fit Omega compliant connectors, and continuity testing
was performed to confirm the contacts pierced the coating and madeelectrical contact with the plated through-hole on the PCB.
The press-fit connectors were installed into PCBs conformally coated with a 0.0006”
thickness of Parylene C (DPX-C) and subsequently tested using a probe test with 100 V, for
10 ohms continuity and 10 MΩ isolation.
Samples were also tested between the contact and the PCB solder pad for interface
resistance using a Fluke Model 1587 FC, with values ranging from a maximum of 0.1 ohms 0.2 ohms.

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To complete the process, contact samples were cross-sectioned
and inspected. The results clearly indicate a positive connection andthat there are no adverse effects of using Positronic press-fit Omega
contacts once parylene coating has been applied.
Conclusion
Press-fit terminations remain a popular termination method to secure connectors to PCBs.
Additionally, more designers are looking to protect their devices against long-term damage.
Positronic has developed a press-fit termination that combines the convenience of pressfit termination with the superior long-term reliability that is afforded by the latest conformalcoatings.
For more information about how Omega press-fit contacts can help transform your reliability,
visit connectpositronic.com or contact us at connectpositronic.com/en/contact/.

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