A Breakdown of Solder Preforms and Their Need for Integration with Lids

Nearly every aspect of heavy industry depends on connections and conduits. These elements hold everything together, particularly within the context of delicate microelectronic items that are small in stature and width but possess the reliable hardiness that engenders performance at mission-critical levels, under any circumstances. Solder preforms provide a strong and guaranteed buffer - a no man's land, if you will - between the raw circuitry and elements within an electronic package and any covering at the top - namely, a lid. 

Yet one can't forget that no two situations in which solder preforms and microelectronic packages might operate will be exactly alike. Because of this, clients will not always know ahead of time the specific attributes of the preforms they need - or the importance of the lid protecting it all. This is where the expertise and track record of AMETEK ECP, as well as the master metallurgists at our Coining division, can assist your business in finding the best possible preforms for your needs, no matter the circumstances of your industry. Today, we'll explore not only the essential attributes of modern solder preforms, and how AMETEK designs them, but also discuss the ways by which integrating them with lids improves overall performance in critical situations. 

A quick refresher on solder preforms 
As outlined by SMT online, solder preforms 
function as the connective tissue in circuit boards, semiconductors and dozens of other electronic assemblies, all of the parts without which the world's most sophisticated technology and machinery could not properly function. Designed and crafted in specific shapes based on client specifications, preforms then are placed within the assembly to form surface-mounted technology pieces. They must be shipped in argon-lined packaging and vacuum-sealed, to best preserve the integrity of the metal within. 

The metallurgists at our Coining facility handle every aspect of preform design and manufacturing in-house, ranging from initial casting and rolling, tooling, die-making, stamping and more. Coining staff, with their combined centuries of experience, can say with complete and utter confidence that they possess the skills to craft preforms and all other metal components using metals ranging from pure gold, silver, copper and aluminum to custom-blended alloys made for clients' special orders.

The key role of the solder lid 
If left open to the elements - exterior or interior - the systems a preform would help operate could easily be rendered useless, of course. This is where lids come into the picture. Solder lids are often created using the Kovar alloy, primarily made of nickel and cobalt plus traces of carbon, silicon and manganese. (It's a common tool of the trade for AMETEK, finding itself in our 
glass-to-metal seals and various other products.) Stainless steel is also common.

Depending on the application, the solder lid can be domed, stepped, "windowed" (usually for optoelectronic applications and sensors more common to the medical device industry) or sealed to the preform itself to form an outer ceramic shell. Here, we arrive at the heart of the matter: What is it about preforms and their various industry uses that makes the implementation of an integrated lid and preform so important, and so much of a better option than its alternatives?

The essentials of assembly 
In a typical application, a microchip or semiconductor chip would be 
surrounded by pieces of solder preform to hold the component in place. A frame of gold-tin alloy surrounds it. The frame is then welded to a lid that's been designed and fabricated with the precise care of Coining experts, with Kovar as its main materials and gold-tin plating flanking it. This process provides for a truly impermeable hermetic seal, one capable of keeping out extreme temperatures in high-heat environments. Our integrated preforms and lids have been tested at eutectic and non-eutectic melting points that exceed 1,000 degrees Celsius: The soldering process itself can be within 20 to 30 degrees of the preform's melting point, so Coining and AMETEK specialists know right from jump that the finished product will meet - and exceed - our customers' expectations.

solder preform use

The case for lid-preform integration 
It's certainly true that the lid covering a solder preform and completing a hermetic assembly does not have to be integrated with the preform; - you wouldn't be breaking any state laws or OSHA regulations by using a different type of package lid. But especially for high-temperature ceramics-based electronic and microelectronic packages, having the preform and its lid bound together in such a manner provides a number of concrete and tangible advantages. Coining metallurgy experts Tao Zhou, Tom Bobal, Martin Oud and Jia Songliang explored this in a research paper sponsored by the Institute of Microelectronics at Tsinghua University in Beijing. 

First and foremost, a ceramic microelectronic package with a gold-tin preform frame will be less susceptible to oxidization than would be the case if the lid were to be attached to the preform but not fully integrated. This holds true even in situations where the surface upon which the package is placed contains moderate-to-high levels of oxidation. Additionally, the ceramic aspect plays a major role in and of itself, supplying the finished product with much of its strength, electrical insulation, high melting point and resistance to the time-driven depredation of corrosion all elements face. For applications such as feed-through in aerospace situations to high-power laser diodes allowing for sophisticated medical imaging and diagnoses, these distinct attributes of lid-integrated solder preforms made from high-quality ceramics make it clear that they're the only option in countless mission-critical industry applications. 

 

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