User-Manual-NeoDen-IN6-Reflow-oven.pdf - 第12页

10 belt speed proportionally if it is t oo l ong, and vice versa. Next, the sha pe of the graph curve must be compared with the desired one (Fig. 2). If the shape is inconsistent, it shall be compared with the following …

temperature rise slope will exceed 2-5 ° C per second, or the reflow peak temperature will be

higher than the recommended one. This may cause excessive crimping, delamination or

burning of PCB and damage the integrity of components.

Today, the most commonly used alloy is Sn63 / Pb37. This ratio of tin and lead makes the alloy

eutectic. Eutectic alloy is an alloy melted at a specific temperature, while non eutectic alloy has

a melting range, rather than a melting point, sometimes called plastic loading state. All

examples described in this paper refer to eutectic tin / lead, which is widely used and has a

melting point of 183 ° C.

The ideal cooling zone curve should be a mirror image of the reflow zone curve. The closer the

mirror image relationship is, the closer the solid structure of the solder joint is, the higher the

quality of the solder joint is, and the better the integrity of the joint is.

The first parameter to be considered in making the temperature curve is the speed setting of the

transmission belt, which will determine the time spent by the PCB in the heating channel. A

typical solder paste manufacturer's parameters require a heating curve of 3-4 minutes. Dividing

the total heating channel length by the total heating sensing time is the accurate transmission

belt speed. For example, when the solder paste requires a heating time of 4 minutes, using a six

foot heating channel length, the calculation is: 6 feet ÷ 4 minutes = 1.5 feet per minute = 18

inches per minute.

Next, it is necessary to determine the temperature setting of each zone. It is important to

understand that the actual zone temperature is not necessarily the display temperature of this

zone. The displayed temperature only represents the temperature of the thermistor couple in the

area. If the thermocouple is closer to the heating source, the displayed temperature will be

relatively higher than that in the area. The closer the thermocouple is to the direct channel of

PCB, the displayed temperature will be more able to reflect the temperature in the area. It is

advisable to consult with the furnace manufacturer to understand the relationship between the

clearly displayed temperature and the actual interval temperature. In this paper, we will

consider interval temperature rather than display temperature. Table 1 lists the interval

temperature settings for typical PCB assembly reflow.

Table 1 temperature setting of typical PCB return section

Area

Temperature Setting

Actual plate temperature at the end of zone

Preheat

210°C(410°F)

140°C(284°F)

Active

177°C(350°F)

150°C(302°F)

Reflow

250°C(482°C)

210°C(482°F)

After the speed and temperature are determined, they must be input to the furnace controller.

Once all parameters are input, start the machine, and after the furnace is stable (that is, all the

actual displayed temperatures are close to the set parameters), the curve can be made. The next

PCB is put into the conveyor belt, triggering the thermometer to start recording data. For

convenience, some thermometers include a trigger function to automatically start the

thermometers at a relatively low temperature, which is slightly higher than the human body

temperature of 37 ° C (98.6 ° f). For example, an automatic trigger at 38 ° C (100 ° f) allows

the thermometer to work almost as soon as the PCB is put into the conveyor belt and enters the

furnace, so as not to cause false triggering when the thermocouple is handled by hand.

Once the initial temperature profile is generated, it can be compared with the profile

recommended by the solder paste manufacturer or the profile shown in Figure 2.

First, it must be confirmed that the total time from ambient temperature to reflow peak

temperature is in line with the desired heating curve residence time, increasing the conveyor

belt speed proportionally if it is too long, and vice versa.

Next, the shape of the graph curve must be compared with the desired one (Fig. 2). If the shape

is inconsistent, it shall be compared with the following graph (Fig. 3 ~ 6). Select the curve that

best matches the shape of the actual shape. The deviation from the left to the right (process

sequence) should be considered. For example, if there is a difference between preheating and

reflow area, first adjust the difference between preheating area correctly. Generally, it is better

to adjust one parameter at a time, and run the curve setting before making further adjustment.

This is because the change of a given area will also affect the result of the subsequent area. We

also suggest that the adjustments made by novices should be relatively small. Once experience

has been gained in a particular furnace, there will be a better "feel" for how much adjustment to

be made.

Figure 3. Insufficient or excessive preheating reflow curve

Figure 4. Too high or too low temperature in the active zone

Figure 5. Too much or not enough reflow

Figure 6. Cooling too fast or not enough

When the final curve is consistent with the desired figure as much as possible, the furnace

parameters should be recorded or stored for later use. Although this process starts slowly and

laboriously, it can finally achieve proficiency and speed, resulting in high-quality PCB

production efficiency.

6. Details about temperature area setting

♦Set the temperature and belt speed to initial value, to the cooling oven, should be preheated

for 25 minutes.

♦When the temperature is stable, let PCB pass heat reflow system. If there is no reflow, can

properly reduce the transfer chain rotation speed. Another way is that, do not adjust the speed,

and increase the temperature properly. When adjust the temperature, notice that it cannot

exceed the PCB and component bearing capacity.

♦Let the PCB pass the reflow system in the new speed or new set temperature. If there is no

reflow, turn to redo the above step. Otherwise, need temperature fine-turning.