164 电容器外壳与灌封件
电容器外壳的工况
电容器外壳长期承受内部电解液侵蚀、内部压力、外部温升（满载 70-105℃）、阻燃要求。
外壳失效的形式是鼓包和漏液，一旦漏液整个电路板报废，所以密封是第一要务。
电解电容与薄膜电容的差别
铝电解电容内部有电解液，外壳要耐电解液 + 耐内压，主流走铝壳 + 塑料套管，塑料件是套管和底座。薄膜电容内部是固体介质，外壳走 PBT 或 PP + 环氧灌封。两种电容的塑料件工况完全不同，不能套用同一个料号。
现场还原：电容在壳里晃荡
2024 年 11 月，乐清一家做开关电源电容的工厂找到我们。他们的固定卡箍和外壳件原来用 PBT，为了降成本换成通用 PA66，结果湿热房测试没过。品质主管的原话：「壳是没裂，但里面的电容都晃了。」
我们把两代件都拿来了。量尺寸：PA66 件在 85℃ 85% 湿热 500 小时后长度方向胀了 0.4%，卡箍抱紧力跟着掉——PBT 同条件下胀了不到 0.1%。根因就是吸水率差了一个数量级，这是材料本性的差距，调工艺调不回来。
我们没让客户退回 PBT 原方案——降成本的需求是真的。给的是低吸湿阻燃 PA66 专用牌，配方里加了矿物填料压吸水率，湿热 500 小时尺寸变化控制在 0.15% 以内，抱紧力保得住，单价还比原来 PBT 低 8%。
三周后复测通过。这个案例的价值在于：换料方向错了，降本就变成了埋雷；方向对了，PA66 在这类件上照样有位置。关键一步是先把失效机理搞清楚，再决定换什么料。
PBT 与 PA66 的分工
PBT 的优势是尺寸稳定和电性能好——吸湿率只有 0.1%，潮湿环境下介电性能几乎不变化，是电容器外壳的首选。PA66 的优势是耐温和强度——热变形温度更高、抗内压能力更强，用于大容量或高温工位。吸湿敏感是 PA66 在这里的短板。
灌封料与壳体的配套
电容器外壳灌环氧树脂，灌封料和壳体的热膨胀系数要匹配。
环氧的线膨胀系数约 50×10⁻⁶/K，PBT 约 100×10⁻⁶/K，PA66 约 80×10⁻⁶/K。
温差 80 K 时会产生内应力，必须选柔性环氧或加缓冲层，否则冷热循环后壳体开裂漏液。
深一层：电容件为什么对吸水这么敏感
电容器件和别的结构件不一样，它对「周围介质环境」有要求。电解电容的容值、损耗这些参数，是在干燥空气里标定的；壳体材料吸水膨胀，几何尺寸变，抱紧力变，散热间隙变，参数就漂。
PBT 在这类件上长期是主流，机理上讲得通：酯键堆得密、结晶度高，吸水率 0.1% 量级，湿热的尺寸稳定性是塑料里最好的一档。
PA66 的酰胺基是亲水基，2.8% 上下的吸水率没法回避——这不是谁家 PA66 做得好不好的问题，是分子结构决定的。
那 PA66 在电容件上就出局了？也不是。分两种情况：对尺寸敏感的部位（抱箍、精密外壳），要么留在 PBT，要么用矿物填充的低吸湿 PA66 改性牌；
对韧性敏感的部位（卡扣、缓冲支架），PA66 的韧性优势反而是 PBT 比不了的——PBT 缺口敏感性高，低温一磕就裂。
所以正确的问题不是「PBT 还是 PA66」，是「这个部位怕什么」。怕尺寸变化走 PBT 路线，怕脆断走 PA66 路线，两个都怕，就轮到改性配方出场——把短处补到工况能接受的水平，把长处留住，这是改性厂和通用料厂真正的分工线。
阻燃与安全认证
电容器外壳必须通过 UL94 V-0，且要通过对应的安规认证（如 UL 810、IEC 60252）。
认证是针对整个电容器做的，不是针对塑料粒子，换料号就要重新验证。
这是很多人踩的坑——以为粒子有 V-0 报告就行了。
长期寿命的隐性变量
电容器寿命标称 2000-10000 h，实际寿命受温度影响极大。
温度每升高 10℃，寿命减半——这条规律同样适用于塑料外壳。
外壳设计要留出散热通道，必要时加导热填料，把壳温压下来比换更贵的料更划算。
工程实测：4 条强制测试
测试1：耐电解液。PBT 在电解液中 1000 h 无应力开裂，PA66 需选耐水解牌号——电解电容优先 PBT。
测试2：灌封冷热循环。-40℃ 到 105℃ 循环 100 次，加柔性环氧的壳体无开裂，硬环氧壳体 30 次开裂。
测试3：阻燃 V-0。PBT 无卤阻燃达 V-0（0.8 mm），PA66 无卤阻燃达 V-0（0.8 mm）——两者均可。
测试4：吸湿影响介电。PA66 饱和吸湿后介电强度下降 25%，PBT 几乎不变——潮湿环境优先 PBT。
追问三连：采购最常问的三件事
一问：灌封件要不要加玻纤。 要区分：灌封外壳要尺寸稳定，矿物填料比玻纤合适——玻纤带来各向异性，固化收缩时翘曲反而大；结构件要强度才上玻纤。看到「增强就是好」的说法要警惕，灌封件加了玻纤再开裂的案例我们一年能见好几起。
二问：阻燃和介电怎么平衡。 阻燃剂加多了介电强度和 CTI 都会受影响。电容器件走 V-0 加 CTI 400 的组合基本够用，更高等级要跟阻燃体系匹配着选，不是等级越高越好——等级上去了、介电掉下来，等于按下葫芦浮起瓢。
三问：壳体壁厚能不能减。 减壁厚省料是常事，但电容壳有耐压和阻燃两道坎：壁厚薄了爬电距离跟着缩短，CTI 等级必须补上去。减壁厚前先算爬电距离够不够，够再做注塑验证，顺序不能反。### 算一笔材料账：电容件的三本账
第一本是料价账：低吸湿阻燃 PA66 专用牌比通用 PA66 贵 12%，一只壳体用料 8 克，单只差价不到一分钱，按年产一百万只算多花不到一万元。
第二本是验证账：通用料在湿热工况下抱紧力衰减，客户现场返修一批按五千只计，拆装人工加物流加赔付合计六万元以上；专用牌的首轮验证费一万二，之后批次免验。
第三本是隐性账：电容壳的失效连带的是电容本体——壳坏电容松，客户未必找壳的麻烦，直接把整个电容判退。供应商层面的信誉损失，是三本账里最大也最没法量化的一本。
三本账合起来，这类「单价低、失效连带大」的件，专用牌的溢价从来不是问题，问题只在于做决策的时候，有没有人把第二、第三本账摆在桌面上。
我们建议供应商给整机厂报价时，直接把三本账做成一页纸——把返修期望值算给客户看，成单速度反而快，因为客户的内部论证环节省了。
边界声明
| 工况 | 推荐材料 |
|---|
| 薄膜电容外壳 | PBT 或 PP + 环氧 |
| 铝电解电容底座 | PBT 阻燃 V-0 |
| 高温工位 | PA66-GF25 耐水解 |
| 大容量抗内压 | PA66-GF30 |
| 灌封配套 | 柔性环氧 + 缓冲层 |
工程备忘
电容器外壳量产前必须做耐电解液 + 灌封冷热循环 + 安规认证三项。换料号就要重新验证认证，不能只看粒子报告。
实战案例：常见踩坑与正解
踩坑一：只看阻燃等级不看 CTI。电容器外壳装在带电回路附近，阻燃 V-0 但 CTI 只有 250 V，长期爬电后表面碳化短路。正解：带电件必须 CTI ≥ 400 V（相比漏电起痕指数），V-0 只解决起火，不解决爬电——这是电气件最常被漏掉的一条。踩坑二：用回收料或副牌料做绝缘件，介电强度批次波动大，耐压测试 5% 击穿。正解：绝缘件一律走正牌新料，批次附耐压报告。踩坑三：端子件装完一段时间扭矩衰减，以为是螺丝松了，实际是尼龙蠕变。正解：电容器外壳承载螺纹连接时必须玻纤增强到 GF25 以上，并在装配 24 h 后复拧一次。
反向案例：一颗灌封件拖垮一个型号
2024 年 5 月，华南某电源厂给一款适配器换灌封件料，从 PBT 换成通用 PA66-GF30，图的是玻纤料便宜两成。
小批量没问题。量产三个月后市场端开始反馈：适配器外壳灌封位开裂，比例大约千分之三。
拉回来解剖，裂缝沿着玻纤取向走——大电流工作下灌封件温度到 90℃ 上下，玻纤取向的收缩差让件在热循环里反复受弯，PA66 基材吸水后又增塑，抗疲劳一掉，裂了。
停线整改花了六周：换矿物填充阻燃牌、修灌封模具浇口、重新做 500 次热循环验证。材料单价其实只差 1 块多钱一颗，型号延期的损失是几百万量级。
这家厂的工程师后来复盘时说：当初只比了物性表上的拉伸和阻燃，没人看「湿热后的尺寸变化」和「玻纤取向」这两行。物性表不会告诉你哪一行会杀死你的产品——那是选料人的活。### 延伸判断：选型前要先确认的三件事
电容器外壳在选料之前，有三件事要先问清楚，顺序错了后面全部返工。
第一：长期使用温度是多少。短时峰值温度和长期工作温度是两回事，物性表上的热变形温度是短时指标，长期工作温度一般要打七折看。
第二：接触什么介质。油、水、清洗剂、汗液、电解液，每一种都会改变料号选择，介质清单比温度表更重要。
第三：有没有认证要求。阻燃、CTI、食品接触、涉水卫生、安规认证，有认证要求的件，换料号就要重新验证，代价远高于材料差价的几十块钱。这三件事问清楚，选料就完成了一半。
把这三件事写成一张表发给供应商，比打十通电话有用——电容器外壳的选型沟通成本，基本都花在这几项反复确认上。
最后一组问答：三个纠结时刻的裁决
纠结一：客户坚持要「指标更好看」的料。 把指标对应到工况再谈：拉伸高十个百分点在电容壳上没有意义，湿热后尺寸变化才是命门。用工况语言替代指标语言，客户的「更好」就会回到「更合适」。
纠结二：PBT 断供时临时切 PA66 行不行。 行，但按「临时」管理：低吸湿牌加全套湿热验证，缺一样都不算切换完成——临时切料的最大风险是「临时」变成了「永久」，验证却停在了第一步。
纠结三：灌封件和壳体要不要同厂采购。 建议同源：灌封和壳体的相容性是系统问题，分属两家供应商时，出问题互相推诿的调和成本，比省下的差价高得多。系统件成套采购，是电容件供应链的成熟做法。### 补记：三个现场判断信号
信号一：湿热测试后抱紧力下降。 先量尺寸再换件——尺寸胀了是吸水问题，换低吸湿牌；尺寸没变但力掉了，看卡扣结构有没有应力集中。
信号二：裂缝沿固定方向走。 典型的玻纤取向问题，浇口方向和受力方向没对上，改模或换矿物填充料。
信号三：灌封件低温脆裂。 PBT 和高玻纤含量的通病，补增韧或换 PA66 系，低温工况必须做 -40℃ 落球确认。### 验证顺序：三步走完再下单
第一步，定部位：把电容件按「怕尺寸漂」和「怕脆断」分成两组，分别对应低吸湿路线和增韧路线，混在一张表里的需求清单先拆开。
第二步，验介质：湿热 500 小时尺寸变化加介电复测，有灌封的做灌封相容性浸泡。数据按湿热后取，干态数据只在规格书里好看。
第三步，盯批次：矿物填充料的批间密度波动要抽测，壳体批差直接反映到装配公差上。三步走完，电容件的选型就闭环了——剩下的是把这套清单固化成来料标准，让流程替人把关。
结语
样品寄出去之后——选料这件事，越早问越省事。
这类件的选料与试模，可以一起聊。
164 Capacitor housing and potting components
Capacitor housing operating conditions
Capacitor housing endures long-term internal electrolyte corrosion, internal pressure, external temperature rise (full load 70-105°C), and flame retardant requirements.
Shell failure forms include bulging and liquid leakage; once leakage occurs, the entire circuit board is scrapped, so sealing is the top priority.
Differences between electrolytic capacitors and film capacitors
Aluminum electrolytic capacitors contain electrolyte inside; the casing must withstand electrolyte + internal pressure. The mainstream uses aluminum shell + plastic bushing, with plastic parts consisting of sleeves and base. Film capacitors contain a solid dielectric, and the casing uses PBT or PP + epoxy potting. The plastic parts of the two capacitors operate under completely different conditions and cannot be used for the same part number.
On-site reconstruction: Capacitor wobbling inside the shell
In November 2024, a factory in Yueqing specializing in switching power supply capacitors approached us. Their fixed clamps and casing parts originally used PBT, but to reduce costs, they switched to universal PA66, but the test in the humid and hot room failed. The quality supervisor's exact words: "The shell didn't crack, but the capacitors inside all wobbled."
We brought in both generations of parts. Dimensioning: After 500 hours of 85°C and 85% humid heat, PA66 pieces expanded lengthwise by 0.4%, and the clamp clamping strength dropped accordingly—PBT expanded by less than 0.1% under the same conditions. The root cause is a difference in water absorption by an order of magnitude, which is a difference in material inherent and cannot be reversed by process adjustment.
We did not ask the customer to return the original PBT plan—the need to reduce costs was real. They provided a special brand for low moisture absorption and flame-retardant PA66, with mineral filler pressure water absorption added in the formula. After 500 hours of humid heat, dimensional changes were controlled within 0.15%, holding firm and holding firm, and the unit price was 8% lower than the original PBT.
Passed the retest three weeks later. The value of this case lies in the fact that if the material change direction was wrong, cost reduction became a hidden pitfall; If the direction is right, PA66 still has a place in this type of part. The key step is to first understand the failure mechanism before deciding which material to replace.
PBT The advantages of the division of labor
PBT compared to PA66 are dimensional stability and good electrical performance—moisture absorption rate is only 0.1%, and dielectric properties hardly change in humid environments, making it the preferred choice for capacitor housings. PA66's advantages are temperature resistance and strength—higher thermal distortion temperature, stronger resistance to internal pressure, suitable for large-capacity or high-temperature workstations. Sensitivity to moisture absorption is PA66's weak point here.
Compatibility between potting material and casing
Capacitor casing filled with epoxy resin, the thermal expansion coefficient of the potting material and the casing must match.
The linear expansion coefficient of epoxy is about 50×10⁻⁶/K, PBT about 100×10⁻⁶/K, PA66 about 80×10⁻⁶/K.
When the temperature difference is 80 K, internal stress will form, so flexible epoxy or buffer layers must be used; otherwise, the shell will crack and leak after hot and cold cycling.
Deeper layer: Why are capacitor components so sensitive to water absorption ?
Capacitor components are different from other structural components; they have requirements for the "surrounding medium environment." Parameters such as capacitance value and loss of electrolytic capacitors are calibrated in dry air; The housing material absorbs water and expands, geometric dimensions change, clamping force changes, heat dissipation gap changes, and parameters drift.
PBT This has long been mainstream for these parts, and the mechanism makes sense: dense ester bonds, high crystallinity, water absorption in the 0.1% range, and dimensional stability in moist heat is among the best among plastics.
PA66's amide group is hydrophilic, and a water absorption rate around 2.8% is unavoidable—this isn't about which brand PA66 is better made, but about molecular structure.
So PA66 is out of the capacitor category? Not really. There are two situations: for areas sensitive to size (clamps, precision housings), either remain in PBT or use low-moisture modified PA66 brand filled with minerals;
For areas sensitive to toughness (clips, cushioning brackets), PA66's toughness advantage is actually something PBT can't match—PBT has high notch sensitivity and cracks at low temperatures.
So the correct question isn't 'PBT or PA66', but 'What is this part afraid of?' If you're afraid of size changes, go for the PBT route; if you're afraid of breakage, go for PA66. If you fear both, it's time for modified formulas to step in—make up for weaknesses to acceptable working conditions, keep strengths. This is the real division of labor between modifiers and general material mills.
Flame Retardant and Safety Certification
Capacitor casings must pass UL94 V-0 and the corresponding safety certifications (such as UL 810, IEC 60252).
Certification applies to the entire capacitor, not for plastic particles; the material number must be revalidated.
This is a common pitfall—thinking particles with V-0 reports are enough.
Hidden Variable of Long-Term Life
Capacitor lifespan is rated at 2000-10000 hours, but actual lifespan is greatly affected by temperature.
For every 10°C increase in temperature, lifespan is halved—this rule also applies to plastic casings.
The enclosure design should leave a cooling channel; if necessary, add thermal packing to lower the shell temperature and reduce the temperature is more cost-effective than replacing with more expensive materials.
Engineering Testing: 4 mandatory tests
Test 1: Electrolyte resistance. PBT does not crack under stress in electrolyte for 1000 hours; PA66 should be hydrolyzed-resistant grade—electrolytic capacitors prioritize PBT.
Test 2: Potting and hot and cold cycles. Cycle from -40°C to 105°C 100 times; shells with flexible epoxy do not crack, hard epoxy shells crack 30 times.
Test 3: Flame retardant V-0. PBT halogen-free flame retardant reaches V-0 (0.8 mm), PA66 halogen-free flame retardant reaches V-0 (0.8 mm)—both are acceptable.
Test 4: Moisture absorption affects dielectric. After PA66 saturated moisture absorption, dielectric strength drops by 25%, while PBT remains almost unchanged—prioritizing PBT in humid environments.
Follow-up questions: The three most frequently asked questions in procurement
First question: Should glass fiber be added to potting parts? Distinguish: The potting shell must have stable dimensions, and mineral fillers are more suitable than glass fiber—glass fiber causes anisotropy, which causes greater warping during curing and shrinkage; Structural parts need strength before using glass fiber. Be cautious when you see the saying 'reinforcement is better.' We see several cases of glass fiber cracking in potting parts every year.
Second question: How to balance flame retardant and dielectric? Adding too much flame retardant affects dielectric strength and CTI. For capacitors, the combination of V-0 plus CTI 400 is basically sufficient. Higher grades should match the flame retardant system—higher grades aren't always better—if the grade goes up and the dielectric drops, it's like pressing a bottle and causing it to float.
Question 3: Can the shell wall thickness be reduced? Reducing wall thickness and saving materials is common, but capacitor shells have two hurdles: if the wall thickness is thin, the creepage distance shortens, so the CTI grade must be improved. Before reducing wall thickness, first calculate whether the creepage distance is sufficient; only then do injection molding verification. The order cannot be reversed. ### Calculating a Material Ledger: The Three Ledgers for Capacitors
The first ledger is the material price account: Low moisture absorption and flame-retardant PA66 special brand is 12% more expensive than General PA66, each shell uses 8 grams of material, with a price difference of less than one cent per unit. Producing one million per year only adds less than 10,000 yuan.
The second ledger is the verification account: General materials lose grip strength under humid and hot conditions, so the customer's on-site repair batch is calculated at 5,000 units, with disassembly, labor, logistics, and compensation totaling over 60,000 yuan; The first round of verification fee for the special brand is 12,000 yuan, with subsequent batches exempt from inspection
The third account is the hidden account: the failure of the capacitor casing inevitably affects the capacitor itself—if the casing is damaged, the capacitor becomes loose. Customers may not bother with the casing and directly reject the entire capacitor. The loss of supplier credibility is the largest and most unquantifiable account among the three accounts.
Combining the three sets of accounts, for these kinds of items with 'low unit price but high risk of failure,' the premium for specialized brands has never been the problem. The problem lies only in whether, when making decisions, anyone puts the second and third sets of accounts on the table.
We suggest that when suppliers provide quotes to OEMs, they directly summarize the three sets of accounts on one page — showing the expected return rate to the customer — which can actually speed up the order process, because it saves the customer's internal verification steps.
Boundary Declaration
| Operating condition | Recommended materials |
|---|
| Film capacitor casing | PBT or PP epoxy |
| Aluminum Electrolytic Capacitor Base | PBT Flame Retardant V-0 |
| High-temperature workstation | PA66-GF25 Hydrolysis Resistant |
| Large capacity and pressure-resistant | PA66-GF30 |
| Encapsulation Support | Flexible epoxy cushioning layer |
Engineering Memo
Before mass production, the capacitor casing must undergo three tests: electrolyte resistance, potting thermal cycling, and safety certification. Changing the material number requires re-validation and certification; you cannot rely solely on the particle report.
Practical Case Study: Common Pitfalls and Correct Solutions
Pitfall 1: Only looking at the flame-retardant rating and ignoring CTI. If a capacitor casing is installed near a live circuit, even if it is V-0 flame retardant but has a CTI of only 250 V, long-term tracking can cause the surface to carbonize and short-circuit. Correct approach: Live components must have CTI ≥ 400 V (compared to the leakage tracking index). V-0 only prevents fire, it doesn’t prevent tracking — this is the most commonly overlooked point in electrical components.
Pitfall 2: Using recycled or secondary materials for insulation components leads to large batch variations in dielectric strength, with 5% failing the voltage withstand test. Correct approach: Insulation components must always use genuine new materials with batch voltage withstand test reports.
Pitfall 3: Torque decreases on terminal components after being installed for a period, often mistaken for loose screws, but the real cause is nylon creep. Correct approach: When capacitor casings bear threaded connections, they must be reinforced with glass fiber to GF25 or above, and re-tightened 24 hours after assembly.
Reverse case: One sealed component drags down an entire model
In May 2024, a power supply factory in South China changed the potting material for an adapter from PBT to general PA66-GF30, aiming to save 20% on fiberglass material.
Small batches are not a problem. Three months after mass production, the market started to provide feedback: the adapter casing at the potting position was cracking, with a rate of about three per thousand.
Pull it back for dissection, the crack follows the direction of the glass fibers—the encapsulant reaches around 90°C under high current operation, and the shrinkage difference along the glass fiber orientation causes the part to bend repeatedly during thermal cycles. After the PA66 substrate absorbs water, it becomes more plasticized, its fatigue resistance drops, and it cracks.
The production line shutdown for rectification took six weeks: replacing the mineral-filled flame-retardant grade, repairing the gating of the potting mold, and redoing 500 thermal cycle verifications. The unit price of the material only differs by a little over one yuan per piece, but the loss from the model delay is on the scale of millions.
The engineers at this factory later said during the review: At the time, they only compared the tensile strength and flame retardancy on the physical property sheet, and nobody looked at the 'dimensional change after humidity and heat' and 'glass fiber orientation' rows. The property sheet won't tell you which row will kill your product—that's the material selector's job. ### Extended judgment: Three things to confirm before material selection
Before selecting the material for the capacitor casing, there are three things that need to be clarified first; if the order is wrong, everything afterward will have to be redone.
First: What is the long-term use temperature. Short-term peak temperature and long-term operating temperature are two different things. The heat distortion temperature on the material property table is a short-term indicator, and the long-term operating temperature is generally considered to be 70% of that.
Second: What kind of medium is it in contact with. Oil, water, cleaning agents, sweat, electrolyte—each will change the choice of material number. The list of media is more important than the temperature chart.
Third: Are there certification requirements? For items with certifications such as flame retardant, CTI, food contact, water health, and safety regulations, if there are certification requirements, changing the material number means re-verification, which costs far more than the material price difference of a few dozen yuan. Asking these three questions clearly means that half of the material selection is completed.
Write these three things into a table and send it to the supplier; it's more useful than making ten phone calls—the communication cost for selecting capacitor enclosures is basically spent on repeatedly confirming these few items.
The final Q&A: The verdict on three moments of dilemma
Dilemma 1: The customer insists on 'better-looking' metrics. Discuss the metrics in relation to the operating conditions: a ten percent increase in tensile strength is meaningless for the capacitor case; the critical issue is the dimensional change after humidity and heat exposure. By replacing metrics language with operating condition language, the customer's 'better' will return to 'more suitable'.
Dilemma Two: Is it okay to switch to PA66 temporarily when PBT supply is cut off? Yes, but manage it as a 'temporary' measure: choose a low moisture-absorption grade and conduct a full set of moisture-heat validations; missing any step means the switch is not complete — the biggest risk of a temporary material switch is that 'temporary' becomes 'permanent', while the validation remains stuck at the first step.
Dilemma 3: Whether to source the potting components and the casing from the same manufacturer. Recommendation: Same source. The compatibility between the potting and the casing is a system issue; if they belong to two different suppliers, the coordination cost when problems arise and each party shifts blame to the other is much higher than the saved price difference. Procuring system components as a set is a mature practice in the capacitor supply chain. ### Additional note: Three on-site assessment signals
Signal 1: Clamping force drops after a damp-heat test. Measure the dimensions first before replacing parts — if the dimensions have expanded, it's a water absorption issue, so switch to a low-moisture-absorption grade; if the dimensions haven't changed but the force has dropped, check whether there is stress concentration in the snap-fit structure.
Signal 2: The crack runs in a fixed direction. This is a typical fiberglass orientation issue; the gate direction does not align with the force direction. Modify the mold or change the mineral filler.
Signal 3: Low-temperature cracking of potting components. Common issues with PBT and high glass fiber content; improve toughness or switch to PA66. For low-temperature conditions, a -40℃ drop ball test must be conducted.### Verification sequence: Complete all three steps before placing an order.
Step one, determine the positions: divide the capacitor components into two groups according to 'sensitivity to size variation' and 'sensitivity to brittle fracture,' corresponding to the low moisture absorption route and the toughening route, and first separate the mixed demand list in one table.
Step two, test the medium: subject it to 500 hours of damp heat, measure dimensional changes and retest dielectric properties. For encapsulated samples, carry out encapsulation compatibility soaking. Data is taken after the damp heat test; dry-state data is only for appearance in the specification.
Step three, monitor batches: the density fluctuations between batches of mineral filler need to be sampled, as the differences between shells directly reflect on assembly tolerances. Once these three steps are completed, the selection of capacitor components is closed—what remains is to solidify this list into incoming material standards, allowing the process to act as a guard for quality.
Conclusion
After sending out the samples—when it comes to selecting materials, the earlier you ask, the easier it is.
The material selection and mold trial for this type of part can be discussed together.
