流焊温度曲线设定)

流焊温度曲线设定类型分为：RSS型的和RTS型的

RSS是升温-保温-回流

RTS 就是升温直接到回流，省去了保温区

RSS：Ramp-Soak-Spike

RSS型基本上适合所有类型锡膏，但不太适合水溶性锡膏，因为保温区锡破坏锡膏的活性而导

致WETTING不好. RSS最大的优势在于保证进入回流时，板上温差达到最小值。如果板上有

过大尺寸元件及连接器，以及PCB比较厚的RSS是比较好的选择。

RTS：Ramp-To-Spike

RTS不仅适用于大多类型锡膏,对于水溶型锡膏是不错的选择。RTS可保证焊点明亮有光泽,因

为RTS在预热过程中,能有效地保护FLUX从而得到比较好的WETTING效果.其次，RTS对老

板来说比较经济,温区少的炉子同样能做出RTS，但做RSS则不甚理想.同样，从工艺窗口来说，

RTS比RSS要宽的多。

最终选用RTS还是RSS，以实际生产的产品为主. 采用什么样的曲线设置方式同时取决于

锡膏类型

RTS才是目前追求的一种最佳工艺方式。RSS是因为以前为了增加锡膏的可焊性，大量的添加

了活性成分，但活性成分恰好又是造成残留的唯一祸手，所以不得不通过回流焊的工艺过程加以

调整，从而多数都采用RSS的方式。

目前市场上主要流行两种profile曲线.

1. 保温型, 这种类型的曲线在soak区可以更好的清洁, 和蒸发flux, 防止焊球产生.

2. 帐篷型, 均匀加热, 达到更好的焊接效果

目前比较流行和最长用的保温型, 但有时候根据焊膏的特性, 需要较短的soak时间,那就只能

用帐篷型了

/wiki/Thermal_profiling

Ramp-Soak-Spike

Ramp-Soak-Spike characteristicsRamp is defined as the rate of change in

temperature over time, expressed in degrees per second.[10] The most commonly

used process limit is 4 °C/sec, though many component and solder paste

manufacturers specify the value as 2 °C/sec. Many components have a specification

where the rise in temperature should not exceed a specified temperature per second,

such as 2 °C/sec. Rapid evaporation of the flux contained in the solder paste can

lead to defects, such as lead lift, tombstoning, and solder balls. Additionally, rapid

heat can lead to steam generation within the component if the moisture content is

high, resulting in the formation of microcracks.[11]

In the soak segment of the profile, the solder paste approaches a phase change. The

amount of energy introduced to both the component and the PCB approaches

equilibrium. In this stage, most of the flux evaporates out of the solder paste. The

duration of the soak varies for different pastes. The mass of the PCB is another

factor that must be considered for the soak duration. An over-rapid heat transfer

can cause solder splattering and the production of solder balls, bridging and other

defects. If the heat transfer is too slow, the flux concentration may remain high and

result in cold solder joints, voids and incomplete reflow.[12]

After the soak segment, the profile enters the ramp-to-peak segment of the profile,

which is a given temperature range and time exceeding the melting temperature of

the alloy. Successful profiles range in temperature up to 30 °C higher than liquidus,

which is approximately 183 °C for eutectic and approximately 217 °C for

lead-free.[13]

The final area of this profile is the cooling section. A typical specification for the cool

down is usually less than −6 °C/sec (falling slope).[14]

[edit] Ramp-to-Spike

Ramp-To-Spike characteristicsThe Ramp to Spike (RTS) profile is almost a linear

graph, starting at the entrance of the process and ending at the peak segment, with

a greater Δt (change in temperature) in the cooling segment. While the

Ramp-Soak-Spike (RSS) allows for about 4 °C/sec, the requirements of the RTS is

about 1–2 °C/sec. These values depend on the solder paste specifications. The RTS

soak period is part of the ramp and is not as easily distinguishable as in RSS. The

soak is controlled primarily by the conveyor speed. The peak of the RTS profile is the

endpoint of the linear ramp to the peak segment of the profile. The same

considerations about defects in an RSS profile also apply to an RTS profile.[15]

When the PCB enters the cooling segment, the negative slope generally is steeper

than the rising slope.[16]

[edit] Thermocouple attachments

Thermocouples are two dissimilar metals joined by a welded bead. For a

thermocouple to read the temperature at any given point, the welded bead must

come in direct contact with the object whose temperatures need to be measured.

The two dissimilar wires must remain separate, joined only at the bead; otherwise,

the reading is no longer at the welded bead but at the position where the metals first

make contact, rendering the reading invalid.[17]

A zigzagging thermocouple reading on a profile graph indicates loosely attached

thermocouples. For accurate readings, thermocouples are attached to areas that

are dissimilar in terms of mass, location and known trouble spots. Additionally, they

should be isolated from air currents. Finally, the placement of several

thermocouples should range from populated to less populated areas of the PCB for

the best sampling conditions.[18]

Several methods of attachment are used, including epoxy, high-temperature solder,

Kapton and aluminum tape, each with various levels of success for each method.[19]

Epoxies are good at securing TC conductors to the profile board to keep them from

becoming entangled in the oven during profiling. Epoxies come in both insulator and

conductor formulations The specs need to be checked otherwise an insulator can

play a negative role in the collection of profile data. The ability to apply this adhesive

in similar quantities and thicknesses is difficult to measure in quantitative terms.

This decreases reproducibility. If epoxy is used, properties and specifications of that

epoxy must be checked. Epoxy functions within a wide range of temperature

tolerances.[19]

The properties of solder used for TC attachment differ from that of electrically

connective solder. High temperature solder is not the best choice to use for TC

attachment for several reasons. First, it has the same drawbacks as epoxy – the

quantity of solder needed to adhere the TC to a substrate varies from location to

location. Second, solder is conductive and may short-circuit TCs. Generally, there is

a short length of conductor that is exposed to the temperature gradient. Together,

this exposed area, along with the physical weld produce an Electromotive Force

(EMF). Conductors and the weld are placed in a homogeneous environment within

the temperature gradient to minimize the effects of EMF.[19]

Kapton tape is one of the most widely used tapes and methods for TC and TC

conductor attachment. When several layers are applied, each layer has an additive

effect on the insulation and may negatively impact a profile. A disadvantage of this

tape is that the PCB has to be very clean and smooth to achieve an airtight cover

over the thermocouple weld and conductors.[19] Another disadvantage to Kapton

tape is that at temperatures above 200 °C the tape becomes elastic and, hence, the

TCs have a tendency to lift off the substrate surface. The result is erroneous

readings characterized by jagged lines in the profile.

Aluminum tape comes in various thicknesses and density. Heavier aluminum tape

can defuse the heat transfer through the tape and act as an insulator. Low density

aluminum tape allows for heat transfer to the EMF-producing area of the TC. The

thermal conductivity of the aluminum tape allows for even conduction when the

thickness of the tape is fairly consistent in the EMF-producing area of the

thermocouple