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The encapsulation of semiconductors like integrated circuits, central processing units, memory devices, and capacitors is actually a fairly simple and straight-forward process. Nine times out of ten, semiconductors are encapsulated by an Epoxy Molding Compound : usually in a transfer molding, or compression molding process.
In both cases, the semiconductor components are placed into the cavity of a mold and then a molding compound is liquefied by heat and/or pressure and pumped into that cavity. This results in the semiconductor being fully enclosed in a protective epoxy shell.
In theory, you then pull the finished encapsulated semiconductor out of the mold cavity and put the next set of semiconductor components in and repeat. However, in practice, stains build-up on the surface of mold die, particularly in the nooks and crannies and along the edges of the cavity. Over time the layer of residue thickens so much it forms a burr along the periphery of the cavity and negatively impacts the quality of the finished part. That's why cleaning and conditioning your molding tools can prevent molding defects.
Epoxy is naturally super adhesive. So along with fillers, pigments, hardeners, and catalysts, an internal release agent is usually also mixed into the final composition of an epoxy molding compound. The internal release agent (usually carnuba wax because of its high compatibility with epoxy) oozes out of the epoxy molding compound as the epoxy itself cures. This allows the final part to release from the mold easily.
However, over time the internal release agent forms a residue, along with other contaminants, and gets trapped in the microporous structure of the metal mold, and eventually oxidizes to form a hard layer. This is the main origin of mold die stains. Other sources include epoxy residue, resin bleed, and solder flux residue.
Eventually this layer of oxidized internal release agent builds up on the mold tools surface: contributing to mold defects, loss of glossy surface quality on the part, and ironically making it harder to release the part from the mold! So obviously, after a certain number of runs, every semiconductor molding operation needs some down time to clean the molds.
Semiconductor mold production lines spit out thousands of finished fully encapsulated semiconductors every few seconds. Not cleaning the build of stains and residue can save you downtime in the short-term but means that at some point you will have to completely stop production to clean your mold dies.
On the other hand, regularly cleaning involves some downtime for some machines, but, in general, production can keep going. The faster you clean the mold the less downtime you will have, and this is the most important factor when trying to fit a cleaning procedure into your production cycle.
A copper brush and some manual labor is still one of the most effective cleaning methods. However, with a mold at 180c or more, how effectively can any line technician really be? And do you really want to turn the mold off to let it cool, then clean it, and then bring it back up to temperature? That would mean hours of downtime. If you have to, then you have to, but there are alternative ways of cleaning the mold die that require less downtime.
Transfer and Compression grade Melamine compounds have been the industry standard for semiconductor mold cleaning a long time now . That’s because they don’t require downtime. Instead, they function like your regular Epoxy Molding Compound pellets: you simply load them into your normal pellet jig and run the machine as you would normally. This means that they can effectively clean your mold during production without shutting down machines. Same goes for compression grade Melamine Cleaning Compound.
Melamine cleans the mold by adhering to stain and peeling it off the surface of the mold when Melamine is peeled off. It also contains an abrasive filler which grinds and attacks stains as it flows through mold die channels and cavities. Another important way it attacks stains is with additives which dissolve the stain and bind it to the Melamine. This reduces the phase boundary between the stain and the mold: allowing the stain to come off more easily when you peel the cured melamine out of the mold cavity.
The semiconductor industry as a whole is, however, moving away from Melamine as a mold cleaning compound. That is because cured Melamine is hard to remove from mold cavities and it produces formalin as it cures. Formalin is an aqueous form of Formaldehyde, and so the vapors produced by Melamine cleaning compound are carcinogenic and very dangerous for human health.
Regulations such as the EU’s REACH places formaldehyde on the substance of high concern list. This makes importing and using Melamine quite legally challenging in some situations. That’s why CAPLINQ’s R&D department is working on developing a new Melamine compound with less than 0.1% formaldehyde to make it meet REACH standards, as well as formaldehyde-free formulations for our melamine cleaning compound.
Because Melamine takes a lot of shots to be effective, is hard to remove from the mold cavity, and gives of formalin vapors that cause cancer, and because manually rubbing at stains with a copper brush is impractical, a new trend within the semiconductor industry is to use unvulcanized rubber compounds .
The unvulcanized rubber compound is then vulcanized in the mold in a process which captures and integrates most mold stains residues. When the now vulcanized rubber compound is removed from the mold cavities it then takes the mold stain with it, leaving a very effectively cleaned mold die surface.
By adding additional cleaning agents such as an imidazole and an imidazoline to the unvulcanized rubber the stains and residue from even the toughest epoxy compounds like biphenyl or dicyclopentadiene epoxy resin can be completely removed. Rubber cleaning sheets can be used with fewer shots, are easier to remove, and are super effective at the right temperature.
However, effective as it is, even rubber has drawbacks. It leaves a very fine layer of residue after the cleaning process. Each of these has their own advantages and disadvantages, but, when used correctly they all are capable of cleaning your molds. When used in combination, they may be even more efficient than one method alone.
Melamine Cleaning Compound is relatively cheap, but requires more shots to be effective and is harder to remove so has overall poorer workability. The fact that it has formaldehyde in its contents makes it more difficult to ship and more dangerous to use. CAPLINQ will continue to research and develop more effective and formaldehyde-free Melamine Cleaning Compounds in the future.
Rubber Cleaning Sheets, on the other hand, gives off fewer vapors, are formaldehyde-free, carcinogen-free, and are more effective with fewer shots, and being easy to removes has excellent workability. However, it does leave a thin rubber residue after use. So, in both cases, the cleaning process is achieved by a combination of chemical and mechanical scrubbing.