Reasons and precautions for welding failure of pulse hot press hot-bar soldering

When debugging the hot-bar soldering machine and during the use of the customer, we often encounter the feeling that the welding is not possible. Through practice, we can analyze it from the following aspects.

1. Flatness of thermode head

In all cases where welding is not possible, the thermode and products to be welded, FPC, FFC and wire are not adjusted smoothly.

The specific reasons are as follows:

1. Uneven tooling and fixture

Cause: sundries on the workbench will affect the parallelism, and it is easy to produce the phenomenon of non melting tin. 

Precautions: it is strictly prohibited to stick tape labels and other articles on the workbench, and it is strictly prohibited to stick tape labels and other articles on the side and bottom of the fixture.

2. When the welding head is pressurized, the bonding flatness between the welding head and the product to be welded is not enough.

When the cylinder of the thermode is pressed down, the force on each point of the support part is not balanced due to the unreasonable design of the tooling and fixture at the bottom, which will also cause the welding head (electrode) to not fully fit with the welding product.

3. The thermode electrode itself is not flat enough

 A. The thermode is not flat enough when it is processed.

 B. The thermode (electrode) has been used for a long time and is oxidized to cause unevenness.

 C. The grinding method of cleaning thermode is incorrect (which will accelerate the wear of thermode), resulting in uneven. Therefore, the thermode is worn and deformed. Please inform the production technology to replace it in time.

2. Poor heat transfer caused by impurities on the surface of thermode head (electrode)

Because the tin has rosin flux, after a long welding time, there will be impurities attached to the thermode electrode, which will cause the heat to not be transferred to the welding products, resulting in insufficient welding heat and poor welding. Therefore, we should always clean the electrode of the thermode. The hot-bar head shall be cleaned with sandpaper (1000-1200 #) every hour. Correct cleaning method: place a parallel block on the bottom of the sandpaper, hold the parallel block and the sandpaper flat against the hot-bar head with both hands, move the sandpaper in parallel to the left and right with slight upward force, and wipe the fine debris with a clean rag after the surface oxide is polished off. Do not touch the temperature sensing wire during cleaning to prevent it from falling off.

3. Unreasonable electrode design causes poor solder climbing and insufficient tension

We use more thermodes during welding, and the welding end face is completely flat. Because a certain pressure is required during welding, tin can not climb through the hole of FPC well. The best solution for this situation is to design the solder head with groove so that the tin can climb up better.