A new specification tackles the application and performance of organic solderability preservatives.
After many years of starts, stops and debate, an industry committee has finally developed a standard for organic solderability preservatives (OSPs). IPC-4555, Performance Specification for High Temperature Organic Solderability Preservatives (OSP) for Printed Boards, is out now, and it was a long time coming.
With the electronics industry fully entrenched in lead-free soldering, a standard for OSP is critical. There are more stringent requirements for solder joint reliability, resistance to corrosion, as well as additional requirements related to complex substrate designs.
The development and acceptance of IPC-4555 dispels the myth all OSPs are the same. With circuit boards fabricated around the globe, and small chemical firms attempting to introduce “new OSP processes,” buyers must be aware. Greater solderability requirements – measured as joint strength, paste spreadability and hole fill – and higher temperatures of lead-free soldering have greatly diminished use of conventional (standard substituted benzimidazole-based) OSPs. With the development of third- and fourth-generation organic solderability preservatives based on a novel aryl-phenylimidazole compound, however, OSP has regained its leadership role as a final finish, particularly in Asia and Europe. In addition, the technology shift to bare copper PWBs with selectively plated gold features requires OSPs that do not tarnish or deposit on the gold.
A case study showed a well-balanced aqueous cleaning agent removed Pb-free, water-soluble tack flux residues better than straight DI water.
Solder bump technology is problematic below 150µm pitch, since it is challenging to manufacture and assemble. As the bump pitch size shrinks, solder bumps have many limitations in the fine-pitch process. Bump printing, plating or bump drops, along with bump pad sizes, are the major constraints; as a result, risk of shorts increases. Today, dies in production have as many as 25,000 bumps per die. It has been predicted this number will increase to 50,000 to 60,000 per die in the next year or two.1
Another form of bump gaining more popularity is the copper pillar. These bumps, instead of being spherical in shape, are in the form of a pillar, with various shapes and sizes. The most popular shape is in the form of a cylinder. The pillar shape allows the high ratio of bump height to bump diameter, therefore permitting very tight pitch, even when bump heights are large. Sometimes a solder cap is formed on top of the pillar to help with connectivity with the mating chip.1 Due to the cylindrical shape and non-collapsing nature of Cu pillar bumps, they can be easily mounted on the fine trace of the laminate. Copper pillars are terminals used to flip-chip IC chips to a substrate in a semiconductor package by thermal compression flip-chip (TCFC) technology. Copper pillars are formed on aluminum electrode pads of an IC chip.
Engineers looking to scale up production are victims of their success if they don’t have a long-term supply chain plan.
The situation: Your engineering team is looking to move from idea to production. You reach out to a contract manufacturer. Question: When does it begin to feel like a partnership?
As a business owner or engineer, working with a contract manufacturer can be daunting, particularly if it doesn’t have experience sourcing challenging parts in a challenging market. How can we as a community of manufacturers help solve this problem? We must put in the time to clearly identify the challenges, set aside time, and build resources to assist customers in real time – and offer a stratified path to a solution based on the type of client. Sounds easy, right? But don’t flinch when it comes to defusing bombs.