Five years, three-fold growth: how Custom Interconnect became the UK’s largest semiconductor packaging and test provider
Five years ago, Custom Interconnect (CIL) turned over £15 million. This June year end, according to Managing Director John Boston, that figure jumped to ‘just a shade under £45 million’ – and the forecast for the next 12 months isn’t just growth; it’s acceleration. “The plan is to grow to £75 million,” John elaborates “Although at the moment, it’s looking more like £82 million which is 84 percent growth.” Ultimately, CIL’s three-fold increase in five years is now on track to become five-fold in six years.
Behind those numbers sits a business gently repositioning itself at the center of UK electronics manufacturing. Formed in 1986, CIL is now the UK’s largest outsourced semiconductor packaging and test (OSAT) company – without actually selling its own products, as John clarifies: “What we effectively sell is processes, not own product. If you look at TSMC or ASE, for example, they’re the world’s largest chipmaker and OSAT and they don’t sell a single product of their own. They have such phenomenal processes that the biggest players in the world go to them.”
Today, CIL’s offering spans three interlinked arms – OSAT, PCB assembly and full product build. “Between 1987 and 1995, we transferred from being a thick film hybrid company to an electronic manufacturing services (EMS) company, and installed four surface mount lines, as that’s where the market was heading,” recalls John. “A big part of our story centers around Eastern Europe, China and the Far East opening up at that time – every customer we grew over a 20–25-year period would eventually move offshore when the project went into the full production phase or they got acquired and again production moved offshore. Interestingly, after the Covid-19 pandemic, we’ve seen almost a complete reversal of that trend, which is a big part of why we’ve grown over the last two or three years.”
Historically, for over ten years, oil & gas downhole electronics previously made up around 40 per cent of CIL’s business whereas today the fraction is closer to ten-to-15 percent. “Electrification is taking over,” John explains. “We’re supporting that transition while the world still depends on oil and gas.” CIL now manufactures professional electronics only, which include medical, defense, aerospace, space, industrial, premium motorsport and transportation. Although the firm’s processes are standardized, every product is customized to the customer designs, and it has built a strong front-end design and modeling capability over the past three-to-four years.
John joined CIL in 1989 as a design engineer, following his early career at STC Defence Systems from 1978 to 1989 as a process engineer working on advanced optoelectronic packaging. “Between 1989-1997 at CIL, I moved through Design Manager, Technical Manager, Production Director and Operations Director. On the morning of 9/11 – not a day you forget – I became Managing Director.” After 47 years’ experience in the industry, he tells us his thoughts on AI and job security: “The threat from AI is out there for everyone, but people forget that in semiconductor packaging, we’re creating the technology in the first place. We are involved in AI infrastructure ranging from the processors, motherboards and GaN power supplies that run them; someone has to make it somewhere!”
Regarding the business’ monumental growth, John reveals there has been a notable shift since the pandemic. “As the global semiconductor crisis hit in 2023, every company started examining its exposure to its own supply chain – particularly China. They haven’t necessarily pulled existing production back, but the next generation of products is increasingly being designed for UK or European manufacture from the outset, provided we can hit the numbers, quality, price and delivery.” CIL’s facility remained open throughout the Covid-19 pandemic, after it was given key worker status manufacturing medical semiconductor packaging for a customer. The company has also been involved in several Innovate UK and Advanced Propulsion Centre (APC) projects, partly funded by UK Government, around electrifying automotive vehicles. “At our peak we had around 11 funded projects running, the largest being APC15@Future BEV with BMW,” he continues. “That combined funding let us invest in capital equipment we couldn’t otherwise have afforded, expanding our process capability significantly. As the funded projects have concluded, CIL has continued the high level of investment”
CIL customers can expect a wide scope of deliverables, solutions and innovations. John highlights how reshoring can make all the difference for clients: “For one customer, a packaged semiconductor device used to pass through 11 different countries before reaching us but we’ve since reduced that to three, significantly cutting their risk exposure and ensuring they get their product.” On technology, CIL offers something that many customers have never seen before – wafer bumping. “About eight years ago, semiconductor assembly shifted from traditional wire bonding, which CIL also does at a rate of 1.5 million wire bonds per week, to attaching solder balls directly to the die at wafer level, then dicing and flipping them to become surface mount devices,” describes John.
“We installed a PacTech SB2+ triple laser wafer bumper – the only one in the UK – and offer device bumping in five alloys: three RoHS-compliant (SAC305, SAC405, SAC-Q), Tin/Lead for military, defense, space and jet engine applications, and Bismuth alloy for biomedical devices that can’t exceed 170°C. This increase in OSAT / EMS customers has seen our surface mount capability grow to eight SMT lines, with a ninth arriving in October 2026. We place one million surface mount components a day and customers increasingly ask us to handle full product build alongside their discrete device and PCBA manufacturing. There’s nothing else quite like it in the UK, or Europe for that matter.” Full vertical integration is an essential part of CIL’s customer experience. “For one customer we package 300mm Silicon wafers into individual devices, mount them alongside other components on a very large and complex PCB, test it, integrate RF amplifiers, and ship a complete 1U 19-inch rack satcom system,” adds John. “They bring us bare die on a wafer and take away a finished product.”
As CIL proudly marks 40 years in business, John reveals the number one factor in its longevity: ability to change quickly. Customer relations are also crucial. “We listen intently to our customers and base the business on what they’re doing,” he concludes. “We remain close to them and stay flexible, enabling us to react quickly at any given moment. Looking to the next five years, our focus will continue to be our people. We run apprenticeships, graduate programs and PhD sponsorships – of roughly 227 people on site, 80 percent are in training or professional development. We’ve been awarded Investors in People recently and more focus will be on staff development and training. We’ve also just completed a deal with global ATE company Chroma, installing two large Chroma test systems in our OSAT facility. This opens the door to UK, European and Scandinavian ‘fabless’ customers needing full characterization of die, packaged devices, and full turnkey production testing.”
