[派瑞林日记]Are Parylene Noodles a Defect

Are Parylene Noodles a Defect

Unlike liquid conformal coatings joined to substrate surfaces by wet application methods, polymeric parylene (XY) uses a unique chemical vapor deposition (CVD) process to assure adherence.  There is no intermediate liquid phase.  Rather, cross-link polymerization of powdered raw XY-dimer converts the solid to a vapor at the molecular level, polymerizing XY directly as a transparent film on assembly surfaces.

Applied in a gaseous state, XY penetrates deep within substrate surfaces, providing an authentically conformal protective covering.  In many ways, parylene coatings are superior to those provided by wet materials like acrylic, epoxy, silicone or urethane, for a wider variety of products and purposes.  Micro-thin film performance makes parylene especially useful for coating printed circuit boards (PCBs) and in microelectromechanical systems (MEMs)/nano technologies.

           The XY deposition process assures neither heat nor cooling is needed for coating adherence.  The circuit board neither expands nor shrinks, reducing coating-stress.  Depositing XY as a dry vapor helps the coated items endure minimal changes during the application process, eliminating another major risk factor of coating defect.

Polymeric Noodles

          As a polymer, parylene begins as a monomer-based linear chain fused covalently.  The ongoing chain entanglements characterizing parylene morphology stimulate a degree of viscoelastic behavior.  Viewed microscopically under normal conditions, they resemble noodles, sometimes elongated but neither precisely straight nor clustered together; often compared to a bundle of spaghetti noodles, they are held together by a few chemical cross-links.  More precisely,

·         the shape of a Gaussian coil develops,

·         collected as parylene (or other polymer) molecules join,

·         ranging from several nanometers to several tens-of-nanometers in length,

·         measured by the root-mean-square end-to-end distance Ree,

·         scaled as the square root of the coil‘s total number of monomers (N) or molecular weight (Mw).

          In this basic form, which encompasses parylene morphology, noodles are NOT a defect, but a normal and characteristic part of the polymer’s physical structure.  Increasing their density across the strands provides shape and strength, limiting their ability to pull away from each other, while increasing their functional and load-bearing uses.  These capacities help XY polymers achieve architectural/performance networks necessary for conformal coating purposes.

Defective Noodling

          Despite its general superiority as a conformal coating, parylene application and use can suffer defects.  While common XY defects can often be identified, planned for and mitigated through proper procedures, they still occur.  Inadequate application or deposition onto a surface unprepared for adhesion can compromise XY function.

Defective noodling is the result of deformation mechanisms developing on the surfaces and interfaces of parylene coated systems.  These factors can cause loss of the parylene film’s surface pattern-effectiveness, disrupting the structural integrity of the coating’s typically reliable noodle-like entanglement.  The surface is then characterized by highly disordered structural configuration, resembling a plate of noodles winding chaotically around each other, interfering with parylene’s usual uniform, pinhole-free surfaces.  Disruption of the coating’s performance integrity can lead to both current leakage and voltage breakdown.

If inappropriately cleaned before application, or inadequately deposited, liquids or other substances can penetrate both at the parylene-substrate interface and through the polymer layer, stimulating an environment of disrupted noodle development.  Film instabilities can also occur on parylene surfaces when temperatures exceed the polymer’s standard glass transition temperatures (Tg).  Basic outcomes include sequential disruption of hierarchical coating formation, a condition that can be generated despite the protection usually afforded by XY’s reliable CVD application method.  Poor adhesion and residual stress can also lead to bending, cracking, peeling and noodling of parylene conformal films.

Parylene conformal coating defects can be caused by a range of factors. However,

·         cleanliness of the product surface,

·         carefully matching the parylene type to the coating assignment/purpose, and

·         expert performance of the CVD process

·         mitigate the potential for these problems to arise.

Undetected trace contaminants disrupt the bond between parylene film and underlying surfaces, leading to disruption of noodle configuration.

Thus, noodles, a basic element of parylene morphology, can themselves be transformed from a tasty dish of conformal coating to one that may need to be scrapped or redone.

·         Conventional, non-defective parylene noodles resemble a properly cooked and stirred pot of spaghetti, with a bit of olive oil stirred in, to keep them from only adhering to each other.

·         Rather, they adhere to the substrate. This recipe can be delicious!!

·         When defects occur, the noodles resemble a tangled mat of unstirred, cooked spaghetti, assuming a random shape, of little use to the conformal coating project.

Not always immediately apparent, disordered adhesion will eventually compromise the coating and, ultimately, the end-product, thus neutralizing parylene’s protective benefits.  As an integral structural XY-component, you can’t avoid the presence of parylene noodles, but you can control them.

译  文

      与根据湿涂法联接到板材表层的液态保形建筑涂料不一样，高聚物聚对二甲苯（XY）应用与众不同的化学气相沉积（CVD）加工工艺来保证黏附。沒有正中间高效液相。反过来，  粉状初始XY-二聚体的化学交联汇聚  将固态转换为分子结构能力的蒸汽，立即汇聚XY做为拼装表层上的保护膜。

XY以汽态涂敷，深层次渗入基材表层内，给予真真正正保形的防护层。在诸多层面，针对更普遍的设备和主要用途，聚对二甲苯镀层好于由例如亚克力，环氧树脂胶，有机硅树脂或聚氨酯材料的湿原材料给予的镀层。微塑料薄膜特性使聚对二甲苯尤其适用涂敷印刷线路板（PCB）和微机电系统（MEM）/纳米材料。

      该  XY堆积  全过程确保既沒有发热量也不用用以涂敷黏附制冷。线路板既不容易胀大也不会收拢，进而减少镀层内应力。将XY做为干蒸气堆积有利于镀层物件在增加全过程中承担最少的转变，清除了镀层缺点的另一个关键风险因素。

汇聚鲜面条

       做为高聚物，聚对二甲苯以共价键稠合的根据单个的网盘直链逐渐。 表现聚对二甲苯形状的已经开展的链  缠结刺激性了一定的程度的粘弹性个人行为。在常规标准下要显微镜观察，他们类似鲜面条，有时候是长细的，但既并不是直的也不是集聚在一起; 通常  与一捆意大利面条对比，他们根据一些热聚合联接在一起。  更准确地说，

·          高斯函数电磁线圈的样子发展趋势，

·          聚对二甲苯（或别的高聚物）分子结构添加时，

·          长短从几纳米技术到几十纳米技术，

·          根据方均根端到端间距Ree精确测量，

·          按比例计算电磁线圈的单个数量（N）或相对分子质量（Mw）的平方根。

          在这类包括聚对二甲苯形状的基本上方式中，鲜面条  并不是  缺点，反而是高聚物物理学构造的一切正常和特点一部分。提升他们在股网上的相对密度给予了样子和抗压强度，限定了他们彼此之间拉下的工作能力，与此同时提高了两者的基本功能和承受主要用途。这种工作能力有利于XY高聚物完成保形镀层需要的工程建筑/特性互联网。

Noodling缺陷

       虽然其做为保形镀层具备广泛的优势，但聚对二甲苯的使用和应用很有可能存有缺点。尽管普遍的XY缺点通常可以根据合理的流程开展鉴别，整体规划和缓解，但他们依然会产生。  增加不充足或堆积在没经粘附的外表上  会危害XY作用。

       有缺陷的镀层是聚对二甲苯镀层管理体系表层和页面上产生的形变体制的結果。这种要素很有可能造成聚对二甲苯塑料薄膜表层图案设计实际效果的损害，毁坏镀层的构造一致性，通常是安全可靠的  鲜面条状缠结。随后，表层的特点取决于相对高度无序的结构结构，类似一张彼此之间盘绕的鲜面条盘，影响了聚对二甲苯通常匀称，无针眼的表层。镀层特性一致性的终断   很有可能造成电流量泄露和击穿电压。

       假如在使用前不适度地清理，或是堆积不充足，液态或别的成分可以在聚对二甲苯 – 底材页面和高聚物层中渗入  ，进而刺激性鲜面条生长发育终断的自然环境。当溫度超出高聚物的规范玻璃化变化溫度（Tg）时，聚对二甲苯表层也会产生膜多变性。基本上結果包含分层次镀层产生的持续毁坏，虽然通常由XY靠谱的CVD运用方式给予维护，但仍可造成这样的事情。黏附性和内应力差也会造成   聚对二甲苯保形膜的弯折，裂开，脱落和涂敷。

聚对二甲苯保形镀层缺点可由一系列要素造成。殊不知，

·          商品表层清理，

·          细心配对聚对二甲苯种类与镀层分派/目地，

·          CVD加工工艺的权威专家主要表现

·          降低发生这种问题的概率。

未检验到的痕量元素污染物质毁坏了聚对二甲苯塑料薄膜和下边的表层间的融合，造成鲜面条配备的毁坏。

因而，做为聚对二甲苯形状的基本元素的鲜面条  自身可以从保形镀层的美味美食变化为很有可能必须损毁或改版的鲜面条。

·          传统式的，无缺点的聚对二甲苯鲜面条类似一切正常煮开和拌和的意大利面条锅，拌和着一点植物油，以避免他们仅互相黏附。

·          反过来，他们附着在板材上。这一菜谱可以很好吃!!

·          当发生缺点时，鲜面条类似未通过拌和的意大利面条的缠结垫，展现任意样子，对保形镀层新项目几乎沒有用途。

并不是总是能马上呈现，混乱黏合最后会危害镀层，最后危害最后商品，进而中合聚对二甲苯的维护实际效果。做为一个完全的构造XY部件，你没法防止parylene鲜面条的存有，但你能操纵他们。

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