密封焊缝密封可实现可靠的焊接和保护电子设备免受恶劣环境的影响

由Mark Sunico.

Seam sealing, or seam welding, is a variation of resistance spot welding most often used to join the lids to the cans of electronic packages. The process uses two motor-driven electrode wheels positioned on opposite sides of the package and rolled along the perimeter, conducting current through both components to create the seal.

Hermetic seam sealing completely seals the package into an airtight metal or ceramic housing using one of two processes: parallel gap resistance seam welding or opposed electrode projection resistance welding. It’s key to manufacturing sensitive microelectronic devices used in industrial and commercial communications, transportation, military and aerospace industries, which often include optical sensors, pressure sensors, communications devices, thermal and laser imaging and power amplifiers.

气密密封这些包装防止了内部的电子元件的劣化，并通过保护这些高敏感的组分免受空气和水分等污染物保护这些高敏感的组分来延伸寿命有用性。可植入的医疗器械，如起搏器和除颤器，也需要气密密封来保护设备和患者。

两种微电子包装

有两种主要类型的包装：金属桶和陶瓷（图1）。

图1：左侧，金属浴缸包装;在右侧，两种类型的陶瓷包装。

The preferred material for metallic tub base packages is Kovar, which has a similar coefficient of thermal expansion (CTE) as glass. The material prevents the metal-to-glass seals of the package’s feedthrough connectors from leaking due to material expansion from heat generated during the welding process.

陶瓷包装由具有钎焊金属密封圈的陶瓷基板制成。科瓦尔也用于陶瓷包装;Kovar以焊接盖子的密封环钎焊到陶瓷基底上。

Parallel Gap Resistance Seam Welding

平行间隙缝焊是执行气密密封的两种方式之一。具有滚轮电极的缝焊机连接到电源，电源通过盖子和包装在电极上传递电流。接缝焊机提供多个重叠焊点，从而产生连续焊接（图2和3）。

FIGURE 2: Schematic of parallel gap seam welding.

FIGURE 3: Schematic showing electrodes and spot welds forming seam.

相对电极投射电阻焊缝焊接

反对电极凸焊使用反对electrodes to join a header, which contains the electronic device, to a cap with a ring or annular projection by running current across the electrodes through both the cap and the header. The heat that’s generated is directed through the projection to weld the parts together (Figure 4).

A successful weld should have at least a 50%-to-90% projection collapse. Linear displacement measuring device sensors, also known as linear variable differential transformers (LVDT), can be added to the weld head to measure this collapse. Additionally, a fillet formation is typically seen at the perimeter of the cap indicating a successful weld.

与平行间隙接缝焊接一样，相对电极投射缝焊接中的金属封装的部件设计非常重要。投影可以在帽或标题上，但是两者之间必须有一个约束特征，因此部件自对准。

Once again, the preferred material is Kovar. For best results, the projection should be located in the middle of the flange, so that as the projection collapses, the displaced material is evenly distributed across the width of the flange.

测试和故障排除

可以进行焊接强度破坏性测试以确保焊缝是安全的。在破坏性测试中，看到至少25％的焊接接头仍然完好无损，在显着的尝试机械地将盖子或底盖从底座上机械地分离后是一个良好的指标，即实现了强烈的焊缝。

Other testing methods include helium fine leak and gross leak bubble testing, optical fine leak detection, internal gas analysis, particle impact noise detection, and temperature cycling.

The Future of Hermetic Seam Sealing

密封缝密封技术对如工业5G商业通信，航空航天和军用电子设备如此苛刻的应用中的成功至关重要。通过焊接确保极好的密封非常重要，并且只有可信赖的焊接设备制造商，占据上述要求的造成措施可以保证高准确可靠的焊缝。

制造商正在将这些标准纳入控制环境焊接技术和开发技术，这将使更高的准确性和焊接成功。密封的未来可能是具有智能视觉系统的机器人辅助接缝密封镐和放置，智能视觉系统具有消除当前误差的边距并导致敏感电子设备的密封性更大的成功。