User-Manual-NeoDen-IN12-Reflow-oven.pdf - 第20页

19 different areas, t he setting temperature of P CBs with few pads i s correspondingly lower. There is also a certain connection wi th the amount of boards released per unit time. However, in normal production, the sold…

Figure 6:Cooling too much/little

When the final temperature profile is as close as possible to the desired profile, tke

record or store of the parameters for later use. Although this process is slow and

laborious at first, it can eventually gain proficiency experience, resulting in high-

efficiency production of high-quality PCBs.

6. Temperature profile setting method

♦Set the temperature of each zone and the speed of the conveyor chain from the initial

value. For cold oven, preheat for ~30 minutes.

♦After the preheating is completed, let the PCB go through the heating soldering

system. If soldering does not occur, the conveyor chain speed can be appropriately

reduced. Or on the premise of not changing the transmission chain speed,increase the

set temperature appropriately, and pay attention to not exceeding the bearing capacity

of the PCB and components when adjusting the set temperature.

♦Let the PCB go through the new conveyor chain under new speed or the adjusted set

temperature,if no soldering occurs,then do the adjustment of the previous step,

otherwise proceed to the next step to fine-tune the temperature profile.

♦The temperature profile can be adjusted appropriately according to the complexity of

the PCB.Can reduce the speed of the conveyor chain and increase the soldering time;

on the contrary, add the speed of the conveyor chain will reduce the soldering time.

♦Generally, when the PCB with components mounted on passes through the soldering

system but is not completely slodered, it can be properly adjusted and then put into the

soldering system for soldering again. Generally, it won’t effect on the PCB and

components.

♦The temperature setting is generally from low to high. If the soldering temperature

range exceeds the set temperature much, should increase the speed of the conveyor

chain or reduce the set temperature.

♦Different PCB boards have different heat transfer rates and heat absorption, then the

heating time and temperature required by soldering are also different. For double-layer

boards and multilayer boards and PCBs with more areas and pads, the setting

temperature is relatively higher , And for single-sided boards or paper plastic boards or

different areas, the setting temperature of PCBs with few pads is correspondingly

lower. There is also a certain connection with the amount of boards released per unit

time. However, in normal production, the soldering machine has its own adjustment

system for general PCB board changes. The soldering machine can be used for normal

production at the recommended temperature during training, unless the heat absorption

of the PCB changes significantly.,then need do adjust accordingly.

7.Temperature Testing Way

♦Attach the temperature thermocouple sensor to a same or similar size PCB to observe

the soldering. Put the PCB to the conveyor chain,then generate the temperature

profile,compare to the recommended temperature profile. If it is same or similar to the

self-adjusting profile, then you can start production, otherwise, according to the

temperature profile, adjust the temperature control area to increase and decrease the set

temperature by about 5 degrees in large temperature difference area, or do

comprehensive adjustment of whole machine to get a temperature profile that can be

used for production work.

♦When starting to put PCB or abruptly change the number of PCB, there is a

difference between the actual temperature and setting temperature. The difference

will turn to normal range when putting the PCB with constant speed for a while.

8. Double sided board soldering instruction

♦Use hot air reflow soldering can finish double-side component soldering. Double-

side soldering design means components are in double-side of the PCB need to

soldering. Double side soldering includes double-side soldering tin and single-side

soldering tin and another side drying glue, as for single-side soldering tin and

another side drying glue, it is easier. First, finish one side’s soldering tin as the

same as single-side, then finish another side tape glue drying in low temperature,

finish double-side SMT craft, after that carry on the next step plug-in or tin process

on craft. Double-side soldering is generally treated as below follows:

♦Start the reflow oven, set up the transfer chain speed controller, finish the A side

components reflow soldering with normal soldering craft.

♦Upend the PCB, repeat normal procedure to mount the component, adopt top

heating strategy to let the B side reflow soldering, but the upend A side has been

reflow soldering, the compounds in thick liquid volatilize, the melting point of tin

is higher than the solder paste, which in order to keep the A side components not

fall out.

9. Trouble shooting

9.1 Soldering analysis

Problem

Possible causes

Solutions be available

Incomplete

reflow

Inadequate heating

lower the transfer chain speed

Shadows from components

a. Increase the transfer chain speed

b. Increase bottom heat

Due to the middle layer of copper foil

Decrease transfer chain speed and increase

temperature

Inadequate

moist

PCB, components without enough solder

paste

Pre-paste to components and PCB

No enough moist time

Increase the temperature of heating zone

PCB bend

Exceeding upper and lower temperature

difference limits

Reduce temperature difference between

preheating zone and bottom temperature zone

Increase transfer chain speed

PCB

discoloration

Exceeding tin temperature on the board,

exceeding temperature gradient or

Increase transfer chain speed

Decrease the preset zone temperature

heating speed

Decrease transfer speed and temperature

Excessive fines

Top layer temperature out of limit

Reduce top heat and increase bottom zone

temperature

Tin balls

Due to dry too fast

Decrease transfer chain speed and temperature

Solder pasting is unqualified or PCB re-

paste

Use PCB after cleaning and drying

Flux coking

Over heating

Add transfer chain speed, lower temperature

Components

wrong position

PNP wrongly, the tin on the solder pad is

irregular or asymmetrical, drying too fast

causes airflow to blow components

Check place position

Check the shape and thickness of tin

Lower transfer chain speed and temperature

Tin bridging

Misposition

Check position

Tin migration

Moist overtime

Increase the belt speed

Lower pre-setting temperature

Solder skips

The solder paste is not enough on pad,

the unevenness of the micro-component,

the PCB coplanarity problem

Thickened tin paste coating

Try to make the solder on the pad even

Check component pin stability

PCB over heat

Heating speed too fast

Decrease transfer chain speed and temperature

Analysis on the cause of the solder joints not shining

In the SMT soldering process, customers will have requirements for the brightness

of the solder joints. It is often just a subjective consciousness of the customer. We

can only get the conclusion of the brightness through comparison. Because there is

no standard for the brightness of the solder joints; roughly speaking, the reasons

for the non-bright solder joints are as follows:

1. There will be difference between the solder paste with or without silver.

Customers should explain their soldering requirements to the supplier when

choosing solder paste.

2. The tin powder in the solder paste is oxidized.

3. The flux in the solder paste has an additive that causes a matting effect.

4. After soldering, there are rosin or resin residues on the surface of the solder

joints, which is a phenomenon we often see in actual work. Especially when

choosing rosin-type solder paste, although rosin-type flux will make the solder

joints slightly brighter than no-clean flux, the presence of its residues often affects

this effect. It is more obvious in larger solder joints or IC foot parts; if it can be

cleaned after soldering, I believe the gloss of solder joints should be improved.

5. The preheating temperature of reflow soldering is low, and there are non-volatile

residues on the surface of the solder joint.

The main reasons for solder joints not full are as follows:

1. The activity of the flux in the solder paste is not enough, and the oxidized

substances on the PCB pads or SMD solder joints are not completely removed.

2. The moisture retention of the flux in the solder paste is not good.

3. PCB pads or SMD soldering positions have serious oxidation.

4. During reflow soldering, the preheating time is too long or the preheating

temperature is too high, cause the failure of flux activity in the solder paste.

5. If the solder paste has not been fully stirred or the flux and tin powder have not

been fully fused. If, there will be insufficient tin on some solder joints.

6. Reflow zone temperature too low.

7. Insufficient amount of solder paste at the solder joint.

9.2 Precautions

*Keep a certain distance of more than 100mm when PCB size exceeds 100mm.

*If the PCB length is longer than the ESD tray, the ESD tray needs to be replaced by