揭秘回流焊：电子产品里的塑料，如何扛住近 300℃高温？
Reflow soldering (also known as reflow welding) is the core process for soldering chips and components on circuit boards in electronic manufacturing.
回流焊（也叫再流焊），是电子制造业中将芯片、元器件焊接在电路板上的核心工艺。
Many people mistakenly think soldering means welding components one by one with a soldering iron. Reflow soldering works in a completely different way.
很多人会误以为，焊接就是拿烙铁点焊元件。回流焊完全不是这样。
The process resembles a high-temperature assembly-line baking process for circuit boards.
它的工作流程更像一场电路板的“高温流水线烘焙”：
Solder paste, a mixture of tin powder and flux, is printed onto metal pads of the PCB circuit board. Automated machines then place chips, resistors, connectors and other SMD components precisely on the pads covered with solder paste.
先在PCB电路板的金属焊盘上印刷一层锡膏，锡膏是锡金属粉末加上助焊剂调配而成；之后机器自动把芯片、电阻、连接器等贴片元件精准贴在涂好锡膏的焊盘上。
After component mounting, the whole PCB board is carried by a conveyor belt into the reflow oven. The oven uses segmented hot air heating and goes through four stages in sequence: preheating, constant-temperature soaking, high-temperature reflow and cooling.
贴装完成后，整块电路板被传送带送入回流炉内部，分段式热风分区加热，依次走完预热→恒温保温→高温回流→冷却四个阶段。
During the high-temperature reflow stage, solder paste melts and wets component leads and PCB pads. The molten solder solidifies after cooling, firmly bonding components to the circuit board.
在高温回流段，锡膏受热熔化，润湿元件引脚与电路板焊盘；等到冷却之后，熔融锡料凝固，元件就牢牢焊接在电路板上。
Here is a key point: reflow soldering does not mean long-duration high-temperature baking.
这里有个很重要的知识点：回流焊并非长时间高温烘烤。
For standard lead-free solder paste with a melting point of 217°C, the peak temperature of most processes ranges from 240°C to 260°C. The materials stay above 230°C for only tens of seconds.
常规无铅锡膏熔点为217℃，工艺峰值温度大多在240~260℃，材料处在230℃以上高温区间的时间只有短短几十秒。
In high-speed optical modules and some Semiconductor packaging scenarios, the peak temperature rises to 270~280°C. A few special processes briefly approach 300°C. This is why many engineers pay close attention to the temperature resistance limit of LCP materials.
像高速光模块、部分半导体封装场景，峰值温度会拉高到 270~280℃，少数特殊工艺，会短暂逼近 300℃，这也是很多工程师会关注 LCP 材料耐温极限的场景。
Then comes the question: why do engineering plastics used for reflow soldering require such outstanding high-temperature resistance?
那么问题来了：为什么能过回流焊的工程塑料，对耐高温性能要求这么苛刻？
Plastic parts on circuit boards, such as connector bases, optical device housings and chip substrates, enter the high-temperature oven together with the whole PCB and endure hot air throughout the process.
电路板上的塑料构件，比如连接器基座、光器件外壳、芯片底座，会跟着PCB整板一起进入高温炉，全程承受热风炙烤。
Once the material cannot withstand the temperature, various failures will occur.
一旦材料耐温不达标，就会出现各种失效问题：
First, softening and warPIng deformation under high temperature.第一，高温软化、翘曲变形。
Common plastics have glass transition temperature (Tg) and heat deflection temperature (HDT). Once exceeding these critical values, the material softens.
普通塑料有玻璃化转变温度Tg与热变形温度HDT，一旦超过这个临界温度，材料就会变软。
Warped components will shift pin positions, directly causing cold solder joints or open circuits and resulting in scrapped products.
零件发生翘曲，引脚位置偏移，会直接引发虚焊、断路，产品直接报废。
The core principle for material selection is that the material’s thermal index must be higher than the peak reflow temperature to maintain dimensional stability under high heat.
因此选型的核心原则就是：材料的热变形指标，必须高于回流焊的峰值温度，才能在高温下守住尺寸稳定。
Second, bubbling, delamination and bursting.
第二，起泡、分层爆裂。
After absorbing moisture from the environment, plastics enter the high-temperature oven. Internal water vapor and low-molecular additives vaporize rapidly, sharply raising internal pressure, which causes surface bubbling and internal structural delamination.
塑料材料吸收环境中的水汽后，进入高温炉，内部水分、低分子助剂会快速汽化，材料内部压力急剧上升，外观出现鼓泡，内部结构分层。
Specialty plastics such as LCP and PPA feature low moisture absorption specifically to avoid bubbling defects during reflow soldering.
LCP、PPA这类特种材料重点强调低吸湿性，就是为了规避回流焊起泡缺陷。
Third, melting, decomposition and carbonization.
第三，熔融、分解碳化。
If the temperature exceeds the melting point or thermal decomposition temperature of the material, the plastic will melt, turn yellow and crack, releasing low-molecular substances that contaminate solder joints and lead to poor electrical contact.
如果温度超过材料熔点或者热分解温度，塑料会直接融化、发黄裂解，释放小分子物质污染焊点，造成电气接触不良。
There is another easily overlooked requirement: resistance to multiple reflow cycles.
还有一个容易被忽略的要求：多次回流考验。
Many circuit boards need components mounted on both front and back sides, so the parts must withstand high-temperature reflow twice. Some complex modules even go through three reflow cycles.
不少电路板正反两面都需要贴装元器件，零部件要经受两次回流高温；部分复杂模组甚至要经历三次。
Materials must endure repeated short-term high-temperature shocks. This is the core value of specialty engineering plastics including LCP, PPA and PPS.
材料必须具备耐受多次短时高温冲击的能力，这也是LCP、PPA、PPS这类特种工程塑料的核心价值。
⚠️ Important reminder: these materials feature short-duration peak heat resistance. They CANNOT work continuously at 260°C for long periods.
⚠️ 这里需要划重点：这类材料是短时峰值耐热，不代表可以长期在260℃环境持续工作。
Take LCP E130I (Polyplastics) and EK106 (Ningbo Jujia) as examples. They can endure tens of seconds at 270~280°C. Under extreme conditions, it can briefly withstand temperatures near 300°C.
就像耐高温的 LCP E130I（宝理塑料）和POLYWEL HPP LCP EK106（常州普威），可以承受几十秒 270~280℃高温，极限条件下短暂触碰 300℃；
However, it will deform and age if kept under continuous baking at 260°C.
但如果长时间放置在260℃环境持续烘烤，依旧会发生变形、老化。
Simple comparison of temperature resistance for common SMT-grade plastics
常见SMT级塑料耐温简易对照
LCP (Representative grade: E130I and EK106): classic SMT-specific material. Normally withstands 270~280°C for short durations. It can approach 300°C briefly under special processes. Certain process risks exist; reflow profile control and pre-drying are required.
LCP（代表牌号 E130I和EK106）：经典 SMT 专用材料，常规短时耐受 270~280℃，特殊工艺可短时靠近 300℃（存在一定工艺风险，需要管控炉温与提前烘干）
PPA: mainstream grade for 260°C reflow, widely used for high-reflectivity LED brackets.
PPA：主流260℃回流牌号，常用于高反射LED支架
PPS: most grades fit 260°C reflow; some premium grades support 270°C
PPS：大多适配260℃回流，部分高端牌号可支持270℃
PA6T/PA9T: high-temperature resistant nylon for SMT, temperature range 250~260°C
PA6T/PA9T：SMT 耐高温尼龙，耐温区间 250~260℃
PBT and ordinary nylon: incompatible with lead-free reflow soldering; they deform and bubble at roughly 230°C
PBT、普通尼龙：无法通过无铅回流焊，230℃左右就会变形起泡
To sum up, reflow soldering is an assembly-line high-temperature soldering process for circuit board components.
简单总结：回流焊是电路板元件的“流水线高温焊接工艺”。
It does not mean the materials are completely heat-proof. Instead, they must survive tens of seconds of high-temperature impact without deformation or bubbling to guarantee stable and reliable electronic products.
不是材料不怕热，而是它们必须扛住几十秒的高温冲击，保证器件不变形、不起泡，才能支撑电子产品稳定可靠。