IPC-A-600H-2010 中文版印制板的可接受性 (1).pdf - 第24页

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 mate…

Target Condition - Class 1,2,3（⽬标条件 - 1,2,3级）

• No pits or voids.

• 无麻点和空洞。

Acceptable - Class 1,2,3（可接受条件 - 1,2,3级）

• Pits or voids do not exceed 0.8 mm [0.031 in].

• Total printed board area affected is less than 5% per either side.

• Pits or voids do not bridge conductors.

• 麻点或空洞不大于0.8mm[0.031in]。

• 印制板每面受影响的区域小于每面面积的5%。

• 麻点或空洞未跨接导体。

Nonconforming - Class 1,2,3（不符合条件 - 1,2,3级）

• Defects either do not meet or exceed above criteria.

• 缺陷不符合或超出上述要求。

图224a

图224b

图224c

2.2 BASE MATERIAL SURFACE（基材表⾯）

2.2.4 Pits and Voids（⿇点和空洞）

15IPC-A-600H-2010 2010年4月

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