The text describes the process of Solder Paste Reflow in Printed Circuit Board (PCB) assembly manufacturing, specifically focusing on Infra-Red (IR) Reflow Soldering.

Here's an extracted and summarized version:

1. The process involves applying a solder paste to tiny Surface Mount Devices (SMDs), which are then temporarily attached to contact pads on bare printed circuit boards.

2. These assemblies are then subjected to controlled heat, causing the solder paste to melt into molten state and solidify again as permanent joints.

Key points about eutectic solders like SN100C:

1. They have uniform grain structures due to melting at a single temperature.

2. This results in bright and shiny appearances after solidification.

3. Unlike non-eutectic solders, they do not corrode steel alloys commonly used in older solder machines.

Comparison with SAC305 alloy (not eutectic):

1. It has a dull, grainy, and cracked surface due to melting over a temperature range rather than at a single point like SN100C.

2. This can lead to corrosion of the steel in older machine parts, especially near heaters or weld joints.

It's also mentioned that once corrosion begins with SAC305, it will continue until there is complete penetration leading to a leak.

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