Using lower temperature and no flash point chemicals to achieve comparable deflashing effectiveness without inducing delamination.
In response to the rising focus on sustainable manufacturing practices and corporate social responsibility, there has been a surge of interest in adopting environmentally friendly and green chemicals for semiconductor manufacturing processes. These alternatives aim to minimize hazards while promoting greater sustainability. Notably, this trend extends to exploring substitutes for conventional chemical dipping deflashing methods, which are employed to address excessive mold bleed caused by the molding process. The assessment of excessive flashes typically involves visual inspection and considers the impact of delamination on the interface between the leadframe and mold compound [1] [2].
Conventionally, these deflashing processes employ high-temperature, low flash point, water-soluble solvents. However, these solvents have drawbacks, including the generation of hazardous fumes, fire hazard risk and substantial electrical power demands for temperature control. This study investigated the feasibility of using lower temperature and no flash point chemicals to achieve comparable deflashing effectiveness without inducing delamination between the leadframe and the mold compound. Typically, manufacturers use solvents such as ethanolamine in figure 1 and diethanolamine in figure 2 as major components for the chemical dipping. By themselves, ethanolamine and diethanolamine have a flash point of 85°C and 134°C respectively [3] [4]. Therefore, the temperature of the chemicals is of utmost importance to ensure that the combined chemicals do not risk any fire hazard. Additionally, the chemical manufacturers also need to ensure that some fire-retardant chemicals are also in place to ensure that no flash point will be observed at all.
Fig. 1: Ethanolamine molecular formula.
Fig. 2: Diethanolamine molecular formula.
Deflashing processes involving chemical dipping are paired with a waterjet process to ensure that the remaining mold flash will be removed completely. The initial stage of chemical dipping uses a solvent to loosen the mold flash, as shown in figure 3. Then, the loosened mold flash is removed mechanically via a high-pressure waterjet. The solvent is important to ensure the effectiveness of the deflashing. For this reason, chemical manufacturers often struggle to balance out the solvent and other additives to ensure that the solvent is effective while at the same time does not pose a fire hazard. Additionally, solvent temperatures also need to be low to ensure that this hazard is further reduced.
Fig. 3: Chemical dipping deflashing process mechanism.
The main purpose of the deflashing process is to remove mold flash on copper surfaces to ensure plating can be done effectively [5]. This study also assessed the results until after plating to ensure the purpose of this process is met accordingly.
Other than chemical dipping, other deflash methods are also often used, such as electro deflashing, but this process is more prone to delamination impact between mold compound and leadframe interface, unlike chemical dipping. Therefore, chemical dipping is the more robust method of deflashing [6].
A study was conducted to understand which chemical types are most efficient to remove mold flashes at different temperatures. Three different chemical types, Chemical A, Chemical B and Chemical C, were evaluated at different temperatures. Chemical A is an existing process that is used for current products. Table 1 shows that Chemical A has a flash point at 130°C, where a fire could be ignited if the temperature overshot until the flash point was reached, which is not that far off. Chemical B and Chemical C are two candidates to replace Chemical A since they do not have flash points and they also have the possibility of working at much lower temperatures.
Table 1: Chemical General Information
| Chemical Type | Flash Point (°C) | Main Solvent Contents (based on Safety Data Sheet) |
| A | 130 | Diethylethanolamine <50% |
| B | None | Ethanolamine <15% & Diethylethanolamine <50% |
| C | None | Ethanolamine < 20% |
Existing processes that use Chemical A are run at 100°C for all products. For this experiment, the temperatures for all chemicals were set at three different temperatures: 60°C, 80°C, and 100°C, as shown in table 2. The constants were set for the dipping time at 20 minutes and the waterjet pressure at 100 bar to understand the effectiveness of the deflashing. Different packages were selected as test vehicles: SO8-FL, PQFN & SOD128 that are all copper alloy based leadframes using different mold compounds. Each test vehicle was run 5 frames per leg.
Table 2: Design of Experiments (DOE)
| Chemical Type | Temperature (°C) |
| A | 60 |
| 80 | |
| 100 | |
| B | 60 |
| 80 | |
| 100 | |
| C | 60 |
| 80 | |
| 100 |
The experiment was conducted in a laboratory scale as shown in figure 4 and figure 5. The leadframe was dipped inside chemical dipping for 20 minutes using different chemicals at different temperatures, as per table 1. Afterwards, the leadframe was rinsed with deionized water and subsequently subjected to a high-pressure waterjet at 100 bar. The leadframe was then dried and visual inspection was performed to observe if any mold flash remained on the leadframe surface.
Fig. 4: Chemical dipping effectiveness experiment.
Fig. 5: High-pressure waterjet setup.
This study focused on the mold flash conditions before and after chemical dipping and waterjet process to observe the effectiveness of the deflashing for discrete SO8-FL package, as per figure 6. The initial checking was performed using a microscope. Additionally, visual inspection was done after tin (Sn) electroplating to ensure that no unseen mold flash remained to cause an unplated leadframe surface.
Fig. 6: Visual inspection pictures of SO8-FL (good condition).
While deflashing effectiveness was initially judged using visual inspection, final judgement occurred after plating to ensure the effectiveness. The judgement criteria are shown in figure 7. For mold flashes, attribute judgement is made based on more than 5% of the lead or pad surface being covered in mold flashes. If the attributive judgement is difficult for borderline mold flash non-conformance, a measurement was performed using a smart scope to determine the percentage of mold flash coverage. For this experiment, all observed failures had more than 50% mold flash coverage, therefore, no additional measurements were done.
Fig. 7: Molding flash remains visual inspection criteria.
The results in figure 8 show that Chemical A, which is an existing chemical, performed well at higher temperatures but failed at low temperature of 60°C for all packages. For Chemical B, mixed results were seen with full functionality for all packages only observed at a high temperature of 100°C. In contrast, Chemical C consistently performed well across all temperatures for all packages.
Fig. 8: Visual inspection results for mold flash after deflashing and plating.
This data shows that Chemical C is more easily activated at lower temperatures compared to Chemical A and Chemical B. A solvent that is not activated will not efficiently remove mold flash. Lower temperature chemicals are advantageous for two main reasons.
The first is lower temperature chemicals are safer than those with higher temperatures. Handling chemicals at higher temperatures is not safe for manufacturing processes as the chemical handlers and machine technicians are at risk of exposure to the high temperature chemicals, causing skin burns. Additionally, lower temperature activation also lowers the fire hazard risk, and less hazardous fumes will be produced.
The second reason is that processing is much more efficient. Higher temperatures require higher heating power. Therefore, higher temperature activation will consume more electric utility power.
In this study, three different chemical types—Chemical A (an existing process), Chemical B, and Chemical C—were evaluated for their ability to remove molding flash at various temperatures. Chemical A, while effective at higher temperatures, failed at 60°C. Chemical B showed mixed results, with full functionality observed only at 100°C. In contrast, Chemical C consistently performed well across all temperatures and packages. Notably, Chemical C has no flash point, making it safer than Chemical A. Lower temperature chemicals offer advantages in safety (by reducing fire hazards and fumes) and efficiency (by lowering heating power requirements).
Lower temperature chemicals, like Chemical C, offer many advantages. They are safer for manufacturing processes, reducing the risk of skin burns for chemical handlers and machine technicians. Additionally, lower temperature processing is more efficient, as it requires less heating power and minimizes utility power consumption. In this case, it is very significant since the process temperature is reduced by 40% from 100°C to 60°C. Overall, Chemical C’s ease of activation at lower temperatures makes it advantageous for effective molding flash removal in molded leadframes. This improvement will benefit semiconductor manufacturing companies in the long term by reducing energy consumption and increasing process effectiveness.
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