User-Manual-NeoDen-IN6-Reflow-oven.pdf - 第9页

7 time is short, it will affect the welding quality, and serious i s causing the solder paste doe s not melt. If the peak temperature is high or the reflow time is l ong, t he met al power will be oxidized and affect the…

♦Power-off

Turn the red power switch to the OFF position and turn off the machine.

♦Change language and the unit of temperature in machine

After the power switch is turned to ON, the NeoDen logo will be displayed on the screen. Long

press the OK button to enter the Debug mode interface. In this interface, you can change the

language and temperature unit of the machine.

5. Temperature wave setting principle

5.10 what is the heating unit temperature?

The heating unit temperature refers to the real-time temperature of the heating plate.

5.11 what is furnace temperature?

Furnace temperature refers to the air temperature between the chain surface and the heating

plate.

5.12 what is PCB surface temperature?

PCB surface temperature refers to the temperature of component welding feet during PCB

welding. (the guiding temperature on the welding curve provided by the solder paste

manufacturer refers to the plate temperature.)

When working, the temperature displayed on the panel is the actual temperature of the heating

unit, which does not represent the temperature in the furnace and the actual temperature of the

board. Therefore, the displayed temperature will be about 20-40 degrees higher than the

temperature in the furnace. The actual temperature is related to the chain speed, PCB size,

thickness, material and component density.

5.1 The reflow soldering theory and the temperature wave

When the PCB goes into heat up area (dry area), the solvent and gas in the solder paste will

evaporate. At the same time, the flux can wet the pad and the component tip and foot. The

solder paste melts, caves in and covers the pad, leading to the pad and component pins insulate

the oxygen. PCB goes into heat preservation area. PCB and components get full preheating. In

case of damaging the PCB and components when it goes into the welding area and the

temperature heats up quickly. When PCB goes into the welding area, the temperature heats up

and the solder paste melts. When PCB goes into cooling area, the liquid solder paste the

soldering points solidify. The reflow process is finished.

The temperature is the key to welding quality. The actual and the setting temperature warming

slope and the peak temperature should be accordant. Before the temperature reaches 160℃,

please control

the heat up speed in about 1℃/S. If heat up too quickly, the PCB and the components will be

damaged, and the PCB may be out of shape. On the other side, the flux volatilizes too fast. And

it is easy to make soldering tin ball. Set the peak temperature 20℃-40℃ higher than the solder

paste melting point. Set the reflow time 10S-60S. If the peak temperature is low or the reflow

time is short, it will affect the welding quality, and serious is causing the solder paste does not

melt. If the peak temperature is high or the reflow time is long, the metal power will be

oxidized and affect the welding quality and serious is causing the component and PCB

damaged.

5.2 The set of the temperature wave

Set according to the temperature curve of solder paste and the welding principle provided

above. Solder paste with different metal content should use different temperature curve, and set

specific reflow temperature curve according to the temperature curve provided by solder paste

manufacturer. In addition, the temperature curve is also related to the density and size of the

heated PCB and components.

In the assembly of printed circuit board (PCB) using surface mount components, an optimized

reflow temperature curve is one of the most important factors to obtain high quality solder

joints. The temperature curve is a function of the temperature on the circuit assembly to the

time. In the reflow process, at any given time, it represents the temperature on a specific point

on the PCB to form a curve.

Several parameters affect the shape of the curve, the most important of which is the belt speed

and the temperature setting of each zone. The belt speed determines the duration of the board

exposed to the set temperature in each zone. Increasing the duration allows more time for the

circuit assembly to approach the temperature setting in that zone. The total duration of each

zone determines the total processing time.

The temperature setting of each zone affects the temperature rising speed of PCB, and high

temperature produces a large temperature difference between the PCB and the zone. The set

temperature of the increase zone allows the board to reach the set temperature faster. Therefore,

a graph must be made to determine the temperature curve of PCB. Next is the outline of this

step, which is used to generate and optimize graphics.

Before starting the curve making process, the following equipment and auxiliary tools are

required: high precision temperature curve instrument (in6), thermocouple (in6), tool for

attaching thermocouple to PCB (mainly high temperature tape) and solder paste parameter table.

There are several ways to attach thermocouples to PCB, the better way is to use high-

temperature solder such as silver / tin alloy, and the solder joints are minimized.

Another acceptable method is fast, easy and accurate enough for most applications. A small

amount of thermal compound (also called thermal conductive paste or thermal grease, which is

often used on computer CPU or graphics card CPU) spots cover the thermocouple, and then use

high-temperature tape (such as Kapton) to stick it.

Another way to attach thermocouples is to use high-temperature adhesives, such as

cyanoacrylate adhesives, which are generally not reliable.

The attachment position should also be selected. It is usually best to attach the thermocouple tip

between the PCB pad and the corresponding component pin or metal end.

(Figure 1. Attach thermocouple tip between PCB pad and corresponding component pin or

metal end)

The solder paste characteristic parameter table is also necessary. The information it contains is

very important to the temperature curve, such as the desired temperature curve duration, solder

paste activity temperature, alloy melting point and the desired maximum reflow temperature.

Before we start, we must have a basic understanding of the ideal temperature curve. In theory,

the ideal curve consists of four parts or intervals, the first three zones are heated and the last

zone is cooled. The more the temperature range of the furnace, the more accurate and close to

the setting of the temperature curve. Most pastes can be reflowed successfully in four basic

temperature zones.

(Figure 2. Theoretically, the ideal reflow curve consists of four zones, the first three zones are

heated and the last zone is cooled.)

Preheating area, also known as slope area, is used to raise the temperature of PCB from the

ambient temperature to the required active temperature. In this area, the temperature of the

product rises continuously at the speed of no more than 2-5 ° C per second. If the temperature

rises too fast, some defects will be caused, such as the tiny crack of ceramic capacitor. If the

temperature rises too slowly, the solder paste will be over sensitive to the temperature, and

there is not enough time to make the PCB reach the active temperature. The preheating area of

the furnace generally accounts for 25-33% of the total length of the heating channel.

The active area, sometimes called drying or wetting area, generally accounts for 33-50% of the

heating channel. It has two functions. The first is to sense the temperature of PCB at a fairly

stable temperature, allowing different quality components to be homogeneous in temperature

and reducing their considerable temperature difference. The second function is to allow the flux

to be activated and volatile substances to evaporate from the paste. The general active

temperature range is 120 ~ 150 ° C. if the temperature of the active zone is set too high, the flux

does not have enough time to activate, the slope of the temperature curve is an upward

increasing slope. Although some solder paste manufacturers allow some temperature increase

during the activation, the ideal curve requires relatively stable temperature, so that the PCB

temperature is equal at the beginning and end of the active region. Some furnaces on the market

can not maintain a flat active temperature curve. Choosing a furnace that can maintain a flat

active temperature curve will improve weldability. Users have a larger processing window.

Reflow zone, sometimes called peak zone or final heating zone. The function of this area is to

increase the temperature of PCB assembly from the active temperature to the recommended

peak temperature. The activity temperature is always a little lower than the melting point

temperature of the alloy, and the peak temperature is always at the melting point. The typical

peak temperature range is 205-230 ° C. if the temperature setting in this area is too high, the