Cold welding is a hermetic sealing process widely used in the crystal, transistor and high powered solid state electronic switching industries.
The cold welding process bonds ductile metals together, by the use of pressure alone, acting through a specific weld tool design. A general flow of metal takes place between the die surfaces at room temperatures, stretching the mating surfaces of the metals. A true homogeneous weld is formed with no introduction of a bonding agent. While most ductile metals can be welded into similar or dissimilar metal joints, some of them are more readily joined together. Aluminium, copper and ferrous metals clad with aluminium or copper flow together with relative ease. Copper or copper clad material must be electro less nickel plated to provide optimum weldability.
The weld zone is not only metallurgically homogeneous, but the metal is work hardened and stronger than the adjacent areas.
Parts are joined without contamination from sparks or dusts and vapours. There can be no contamination from fluxes, solders or brazing alloys which are traditionally used in certain industry sectors. The interior of an enclosure is as free from contamination after welding as it is before. Since no heat is required or generated during welding, the contents of the enclosure are not subjected to temperature cycling.
Cold weld enclosures are truly vacuum tight. While ordinary specifications call for seals with a Helium leak rate of 10-9 cc/sec/atm. Radiflow tests have been made on cold welded enclosures without detecting leaks at the instrument threshold of 10-11 cc/sec/atm.
The weld can be made in an optimum environment for a given product, eliminating secondary pump-out operations. Seals may be made in high or low vacuum, dry nitrogen or other desired atmospheres at predetermined pressures.
The cold weld press consists of a 4 post arrangement allowing a stable and repeatable platform for cold welding. A 12 ton press has the capacity for welding most all standard device packages covering crystal and transistor outlines. Larger tonnage presses of either 20 ton or 40 ton are also available to cover multiple package welding, utilising multiple dies, and for the sealing of large diameter SCR devices (some as large as 5" in diameter).
The press system consists of a press base, mounted and sealed within the stainless steel glove box (optionally supplied mounted on a free standing bench assembly). The four posts extend through the top of the glovebox and support the press crown assembly. Tonnage is developed by an air-hydraulic booster and operates on 100psi or less. This arrangement of hydraulic cylinders, oil reservoir, tools and boosters allows a low pressure ram advance for closing the welds tools and a short high pressure stroke for cold welding. Tonnage can be held indefinitely without oil heat up problems.
The precision weld tools consist of upper and lower weld dies which are permanently aligned and mounted on a precision two post die set. This method assures long life and optimum alignment. A floating adapter on the press ram seats in a tee slot atop the weld tool assembly eliminating any miss-guidance. Brass bushings on guide posts minimise lubrication contaminants within the clean atmosphere. The weld tools are designed for particular part configurations, considering material, material thickness, geometric shape, deformation characteristics, feed through requirements, finished dimension needs and reduction requirements in the weld area. Package design should consider requirements and limitations of the cold weld method in early stages of development. Each weld tool is machined from high-carbon-high-chrome tool steel and hardened, ground and polished with tolerances on some dimensions held to plus or minus .00025". The tools are tested for alignment, deformation and weld performance before shipment. Both upper and lower weld dies have a standard 2 1/4" diameter and 2.2" length. Dies have 'O' rings grooves in sides and bottoms for use with vacuum die set chambers. This die size is adequate for most all standard electronic device packages and will withstand the repeated application of 12 ton loads for many hundreds of thousands of welds.
When an evacuated device is required during the weld cycle, stainless steel vacuum chambers can be added to the weld tool. Dual interlocked safety pushbuttons are used to initiate a spring loaded upper and a stationary lower vacuum chamber surround the weld dies. The low pressure down stroke of the press ram is resisted by springs, allowing the vacuum chamber to be sealed for evacuation and backfill (nitrogen/helium) without applying pressure to the parts to be welded. This process cycle is PLC (Programmable Logic Controller) operated and allows adjustable vacuum and backfill gas time delays.
The PLC is interlocked with pressure monitoring and automatic vacuum pump operation facilities. Complete evacuation and backfill are assured via ports in the tooling. The upper weld tool cavity retains a part by means of spring-ball plungers. Once the required vacuum level within the chamber is achieved the vacuum instrumentation will interface with the PLC to allow the weld follow through of the press at the correct time. The vacuum system provided is based on customer=s requirements and Pyramid can provide pumping options covering rotary, turbo drag, turbo molecular and cryogenic vacuum pumps. Vacuum levels to 2 x 10-6 mbar are achievable based on pumping system and time of process. All vacuum systems are supplied with all necessary valving, vacuum instrumentation, interconnections and fittings.
Full environmental glovebox systems with suitable pre-process vacuum gasbake oven(s) can be supplied.