IPC-A-600H-2010 中文版印制板的可接受性 (1).pdf - 第25页

Brief summary of the Second IPC Blue Ribbon Committee on Measles This second committee was formed in late 1978. This committee reviewed the findings of the first committee, solicited the industry for additional data, and…

This section is focused on those subsurface conditions of laminated

base materials that are externally observable through the base mate-

rial itself and some solder mask coatings. The most frequent sub-

surface base material conditions are termed measling, crazing,

delamination, blistering and foreign materials. These conditions

may be observed throughout the printed board manufacturing and

inspection process; such as:

• During incoming metal-clad base material evaluations after being

manufactured by the laminator,

• By the printed board manufacturer after having removed (etched)

the metal cladding in the preparation of ‘‘innerlayer’’ details for

multilayer printed boards,

• After etching the ‘‘outer’’ layers of printed board to form the

required arrangement of conductive patterns and markings,

• After baking operations (such as solder mask or component leg-

ends),

• After thermal shock, as in solder fusing/coating or solderability

testing processes.

Base material subsurface conditions have been the subject of con-

siderable discussion within the printed board industry for several

decades. Of the several subsurface conditions, measling and craz-

ing continue to cause the most concerns. Measles and crazing have

been the primary focus of three IPC ‘‘Blue Ribbon Committees’’ of

experts. The following are brief summaries and additional com-

ments from the IPC Blue Ribbon Committees:

本节重点介绍透过基材本身和某些阻焊膜涂覆层从外表可观

察到的层压基材表面下的状况。最常见的基材表面下状况

有：白斑、微裂纹、分层、起泡和外来夹杂物。这些状况可

在印制板整个生产过程和检验过程中发现，例如：

• 在来料检验基板生产商制造的覆金属箔基材时；

• 在印制板生产商蚀刻金属箔后为多层印制板制备“内层”图

形的过程中；

• 为了形成所需导电图形和标记，蚀刻印制板“外”层之后；

• 烘干操作（例如阻焊剂或元器件字符）之后；

• 热冲击之后，例如焊料热熔/涂覆或可焊性测试过程中。

几十年来，基材的表面下状况已成为印制板行业内不容忽视的

论题。在这些表面下状况中，白斑和微裂纹一直最受关注。

白斑和微裂纹已成为三届IPC“蓝带委员会”专家所关注的焦

点。下面是IPC蓝带委员会的概述和补充说明：

Brief summary of the First IPC Blue Ribbon Committee on

Measles

This first committee conducted a wide overview of printed board

base material surface and subsurface conditions with a major focus

on measles. IPC's ‘‘Measles in Printed Wiring Boards, Information

Document’’ was published in 1973 as a result of this effort. The

committee was to collect as much data as was available on measles

and other surface/subsurface conditions; and to standardize the

terms, definitions (descriptions), photographs, and illustrations of

surface and subsurface conditions. It was felt that sufficient

research had been done by industry and that a position on

‘‘measles’’ could be prepared by the committee. The committee's

recommendation was as follows, ‘‘comprehensive review of avail-

able literature and available research and test data, that while

measles may be objectionable cosmetically, their effect on func-

tional characteristics of finished products, are at worst minimal,

and in most cases insignificant.‘‘

Comments: Despite the committee's recommendation and industry

data, there was still a strong reluctance by most government and

industry personnel to accept that measles are a cosmetic condition

with no functional effect in most applications. Most companies

continued to retain ‘‘no measling’’ requirements in their specifica-

tions. But when measles or other nonconforming surface/

subsurface conditions had severe impact on their production sched-

ules, the customer (or acceptance agency) would produce a

document that established acceptance guidelines for measles (and

frequently other surface and subsurface conditions). The new

guidelines were based on size, percent reduction in conductor spac-

ing, and amount of affected area. They also varied from customer-

to-customer. As technology evolved, in particular reductions in

conductor spacing, the effect of measling and other surface/

subsurface conditions once again became a serious industry wide

concern. As a result, a second IPC Blue Ribbon Committee on

Measles was formed.

第⼀届IPC蓝带委员会关于⽩斑的概述

首届委员会对印制板基材表面和表面下的状况，主要是白斑

方面，进行了广泛的探讨。IPC于1973年发布了作为该项研究

的成果—《印制电路板中的白斑，报告文献》。该委员会旨在

尽可能多地搜集现有的关于白斑以及其他表面/表面下状况的

资料，并标准化其术语、定义（说明）、照片以及图例。委员

会认为业界已做了充分的研究，委员会可以为“白斑”作结

论了。委员会的建议如下：“根据对现有文献和研究及测试

数据的综合考察表明，从外观上讲，白斑可能是不美观的，

但即使是最严重的白斑，对成品的功能特性的影响也是极微

小的，且大多数情况下是无足轻重的”。

说明：尽管有委员会的建议和业界的研究数据，仍有多数政

府及业界人士强烈抵制，他们拒不接受白斑只是一种外观上

的状况，在大多数应用中无功能性影响的观点。多数公司的

规范中仍保留“没有白斑”的要求。但是当白斑或其他不符

合的表面/表面下状况严重影响其生产进度时，用户（或验收

部门）就会行文制订白斑（通常包括其他表面和表面下状

况）的验收导则。新的验收导则以导体间距减小的尺寸、减

小的百分比，以及受影响面积为基础，具体要求因用户不同

而异。随着技术的发展，尤其是导体间距的减小，白斑及其

他表

面

/表面下状况的影响再一次成为业界关注的焦点。因

此，关于白斑的第二届IPC蓝带委员会应时而生。

2.3 BASE MATERIAL SUBSURFACE（基材表⾯下）

Introduction（引⾔）

16 IPC-A-600H-20102010年4月

Brief summary of the Second IPC Blue Ribbon Committee

on Measles

This second committee was formed in late 1978. This committee

reviewed the findings of the first committee, solicited the industry

for additional data, and reviewed the proprietary acceptance crite-

ria provided by IPC members. The Second Blue Ribbon Committee

came to the same conclusion. Measles are a cosmetic process indi-

cator and had almost no reported effects on a product's functional

performance in most applications. The major exception was high

voltage applications. There was still reluctance by some govern-

ment organizations and a few industrial companies to categorically

accept measles. As such, this committee established a set of

measling/crazing requirements that obtained consensus from all

IPC members. The result was a matrix of acceptance limitations for

the three major phases of the printed board electronic assembly

process: laminated material, printed board final inspection, and

after printed board assembly. These requirements included percent

reductions in conductor spacing (not exceeding minimum conduc-

tor spacing), and various amounts of measled area for each side of

the printed board (or assembly) based on the Class of product.

These requirements were added as an amendment to the first print-

ing of the IPC-A-600, Revision C, and were included in later print-

ings of the C revision and, in a different format, the IPC-A-600,

Revision D.

Comments: The primary concerns expressed by the reluctant indi-

viduals are summarized in the following list (with comments):

• Electrical Insulation Resistance, both volume and surface - sev-

eral reports and available test data indicates that insulation resis-

tance is not significantly affected by measling or crazing.

• Contamination - the concern was that ionic materials could dif-

fuse or be ‘‘pumped’’ (by alternating atmospheric pressure) into

measles or crazing and would result in lower insulation resistance

or conductive anodic filament (CAF) growths, shorts. Salt spray

tests indicated this was not a valid premise, and most ionic mate-

rials (such as salts) will not diffuse into the base material.

• Applied Voltages - high voltage applications are a concern (in

particular where there is the possibility of ‘‘corona’’ in the mea-

sling or crazing) the dielectric strength is reduced by 20-50% in

comparison to a similar non-measled/crazed area, in particular at

altitudes greater than 20 km [12.43 miles].

• Environmental - most measling/crazing did not appear to increase

in size or occurrence due to environmental testing.

IPC-A-600, Revision E, was the first revision to reflect the needs

for surface mounted component technology. As such, the accep-

tance requirements for measling and crazing were separated. For

measles, the acceptance requirements allowed bridging under sur-

face conductor spacing. This was done based on the definition of

measles, test data, and industry experience of measles having never

been documented to cause a functional failure. Crazing is much less

controlled separation in the base material forming ‘‘interconnec-

tions’’ between measles and possibly adjacent conductive patterns;

therefore, the acceptance requirements for crazing were set the

same as the similar conditions of delamination and blistering.

Over a period of time, governing specifications have become

excessively heavy regarding the presence of measles. In addition,

cosmetic appearance has become a major acceptance criterion. In

actual fact, no failure has ever been attributed to measling, based on

all military and industry testing to date. IPC, industry and various

military agencies have conducted extensive testing in severely

measled assemblies under extreme environmental conditions for

long periods of time with no evidence of growth, spreading or any

detriment to the function of the assembly. Measles should not be

the cause for rejection.

Measling is an internal condition occurring in the woven fiber rein-

forced laminated base material in which the bundles are separated

at the weave intersection. The term ‘‘crazing’’ is sometimes used to

describe an array of measles which appear from the surface to be

interconnected. When the measles look to be interconnected, this

condition called ‘‘crazing’’ is a form of delamination in that there

are separations along the length of the fiber/yarns and the resin. For

non-woven material, this condition resembles a measle but is ran-

domly located and has an irregular shape (see Figure 23a).

In a case study done, the prime cause of the observed measles was

a combination of moisture, which diffuses readily into epoxy-glass,

and component soldering temperatures. The application of local

high temperatures for component mounting caused entrapped

moisture to vaporize and break the epoxy-glass bond at the

‘‘knuckle’’ (intersection of the warp and fill of the e-glass cloth).

From previous experience, it is known that epoxy-glass absorbs

atmospheric moisture, and when moisture content exceeds 0.3

wt%, it can give rise to measling during solder dip/level and/or

assembly soldering operations.

There are other factors that can contribute to measles/crazing such

as: resin composition, method of making laminates, coupling

agents, T

, etc. In the past, reports were compiled which revealed

that measles and crazing with over 50% spacing violation were not

adverse to the reliability of the hardware. Why, if all test reports

showed no problems with measles and no reported field failures,

are we so concerned about measles and crazing? Because it appears

feasible, in theory, that if measles with 100% conductor spacing

violation combines with moisture or some other contaminant, cop-

per migration (IR failures) should be experienced between conduc-

tors.

2.3 BASE MATERIAL SUBSURFACE（基材表⾯下）

Introduction (cont.)（引⾔（续））

17IPC-A-600H-2010 2010年4月

Even when the potential failure mechanism mentioned above is

analyzed, it is almost impossible to experience such (IR/ migration)

failure. First, a measle(s) gapping conductive patterns is needed.

Secondly, moisture in the printed board/ assembly, along with a

conductive or ionic contaminant such as chlorides, is necessary.

In this instance, a typical industry example, the measle is at the

center between two plated through holes (see Figure 23b). The

measle is 0.4 mm [0.0157 in] wide. In order to get possible copper

migration, the measle had to gap the two plated through holes. This

of course would be most unlikely. The second example (see Figure

23c) illustrates what is required for a potential failure mechanism

between two surface conductors. A (+) conductor directly over a

knuckle is required and a (-) conductor is also required directly over

a knuckle. For an electrical short to occur between these conductors

through the base material, there would need to be a conductive path

from one conductive pattern, through the remaining dielectric

materials (resin and yarn) to the separation (measle), along the

separation in the direction of the other conductive pattern, once

again through the remaining dielectric materials (resin and yarn),

and to the second conductive pattern. In order to induce a failure all

of the above mentioned ingredients are required along with a volt-

age potential between two adjacent conductors. This occurrence is

highly unlikely and is most likely why the industry has not experi-

enced any adverse reliability problems due to measles.

When making acceptance calls on electronic hardware, consider all

the possible concerns mentioned above. Measles should not be con-

sidered a nonconforming condition. It should instead be considered

a process indicator, telling you that the process is on the verge of

going out of control. Correct the problem, but do not scrap the

product, taking into account all of the above mentioned variables.

第⼆届IPC蓝带委员会关于⽩斑的概述

第二届委员会成立于1978年底。它复审了第一届委员会的发

现，向业界征寻了更多的数据资料，并审阅了IPC会员提供的

专有验收准则。第二届蓝带委员会得出了同样的结论。白斑

是一种外观性的制程警示，在大多数应用中，几乎没有任何

有关影响产品性能的报道。一个主要的例外是高压电应用。

此时仍有一些政府机构和业界公司反对无条件地接受白斑。

因此，该委员会制定了一套由所有IPC会员一致同意的白斑/

微裂纹要求。形成的验收要求适用于印制板电子组装过程中

三个主要阶段：层压板材料、印制板终检和印制板组装后。

这些要求包括导体间距减小的百分比（不超出最小的导体间

距）和基于产品级别的印制板（或组装件）每面的白斑区域

的大小。这些要求作为修订本补充到IPC-A-600C版的首印版

中，并纳入IPC-A-600C的再版中，且在IPC-A-600D版中以不

同形式出现。

说明：反对方阐明的主要顾虑归纳如下：

• 电气绝缘电阻，包括体积电阻和表面电阻 - 一些报告和现

有的测试数据都表明：绝缘电阻受白斑或微裂纹的影响不明

显。

• 污染 - 离子残留物可能会扩散或被“抽吸”（由于大气压发

生变化）到白斑或微裂纹中，并会导致绝缘电阻的降低或导

电阳极丝（CAF）的生长进而短路。盐雾测试表明，这个根

据不能成立，大多数离子物（例如盐）不会扩散到基材中。

• 所用电压 -高压应用关系是一个顾虑（尤其是白斑或微裂

纹中可能出现“电晕”的情况下），与类似的无白斑/微裂纹

区域相比，有白斑/微裂纹的区域的绝缘强度降低了20%～

50%，尤其在20km（12.43英里）以上的海拔高度下。

• 环境

- 大

多数白斑/微裂纹不会因环境测试而增加或尺寸扩

大。

IPC-A-600E版本是第一个反映表面贴装元器件技术需求的修

订版。因此，对白斑和微裂纹的验收要求便分开了。就白斑

而言，验收要求允许其跨接表面导体间距。这样规定基于白

斑的定义、测试数据，而且业界的经验中从来没有白斑导致

功能性失效的记载。微裂纹是产生于基材内的一种更不受控

的分离现象，形成白斑间的互连，其范围可能跨接相邻的导

电图形，因此，对白斑的验收要求与类似的分层和起泡状况

相同。

相当长一段时期，一些指导规范过于看重白斑现象。再者，外

观也成为一个主要的验收准则。事实上，迄今为止，根据所

有军方及工业界当前测试发现，白斑从未导致过任何失效。

IPC、业界及各军方机构在极端环境条件下，对出现严重白斑

的组件进行了广泛的测试，并没有发现白斑有增长、扩散或

有损于组件功能的现象。白斑不应该作为拒收的理由。

白斑是发生在编织纤维增强型层压基板内的一种内在现象，

基材内的纤维纱束在交叉处的粘合发生分离。“微裂纹”一

词有时用来描述表面上连成片的白斑阵列现象。这种称作微

裂纹的互连的白斑，其实是分层的一种形式，即纤维纱线沿

其长度方向与树脂发生了分离。对于非编织的材料，这种情

况类似于白斑但是随意排列且形状不规则（见图23a）。

在一项研究案例中，所观察到的白斑现象主要成因是能快速

扩散到环氧玻璃中的湿气和元器件焊接时的温度共同作用的

结果。元器件贴装时产生的局部高温造成裹挟的湿气蒸发，

并破坏环氧玻璃在“接合点”（环氧玻璃布经线与纬线交叉

处）的粘合。根据以往的经验，我们知道环氧玻璃会吸收大

气中的湿气，当湿气含量超过0.3%（重量比）时，在浸焊/热

风整平和/或组装焊接作业中会使白斑增加。

2.3

BASE

MATERIAL SUBSURFACE（基材表⾯下）

Introduction (cont.)（引⾔（续））

18 IPC-A-600H-20102010年4月