IEC 61188-1-1:1997 pdf download.Printed boards and printed board assemblies – Design and use – Part 1-1: Generic requirements – Flatness considerations for electronic assemblies
1 Scope
This part of IEC 61 1 88 describes those factors which control the flatness of rigid printed
boards and their assemblies. The object of this standard is to inform the designer,
manufacturer, assembler and user of rigid printed boards and their assemblies about those
factors affecting their flatness. This standard incorporates advice regarding:
– design (clause 3);
– base material (clause 4);
– unassembled printed boards (clause 5);
– printed board assemblies (clause 6).
2 Normative reference
The following normative documents contain provisions which, through reference in this text,
constitute provisions of this part of IEC 61 1 88. At the time of publication, the editions indicated
were valid. All normative documents are subject to revision, and parties to agreements based
on this part of IEC 61 1 88 are encouraged to investigate the possibility of applying the most
recent editions of the normative documents indicated below. Members of IEC and ISO maintain
registers of currently valid International Standards.
IEC 61 1 89-2: 1 977, Test methods for electrical materials, interconnection structures and
assemblies – Part 2: Test methods for materials for interconnection structures
3 Basic requirements
3.1 Design
The designer of the rigid board/assembly shall aim to achieve a mechanically balanced
construction. For the printed board, balanced construction pertains to the even distribution of
the amount of resin, reinforcement and metallic foil about the centre of the board in any axis. In
addition, if metal is bonded to the substrate (e.g. as a heat sink) the contribution to flatness
provided by the metal must be understood.
Printed board assemblies usually have components on only one side. However, with the advent
of surface mounting, many designs have both sides of the board populated with components.
Proper location of components by size, weight and the number of leads to be attached to the
board will improve the flatness characteristics of the assembly.
3.2 Rigid board manufacture
The rigid board manufacturer shall consider how to use and process the material to minimize
distortion.
3.3 Assembly
The rigid board assembler shall try to ensure that no distortion is introduced, particularly during
soldering and handling operations.
3.4 Use
The user shall, by good storage and equipment practice, minimize the likelihood of distortion
occurring after assembly.
4 Deviations from flatness – Rigid copper-clad base material
4.1 Causes
The following can contribute, either singly or in combination, to distortion of copper-clad
material.
4.1 .1 Reinforcement
Glass fabrics may be stressed during weaving and treatment. Distortion of the laminated
product introduced by individual sheets of stressed glass fabric will be small.
4.1 .2 Copper foil
The effect of the copper foil on distortion is usually small.
4.1 .3 B-stage material (prepreg)
Impregnation of the reinforcement with resin, which is subsequently partially cured, produces
“B-stage” base material (prepreg). Non-uniform impregnation can produce stresses which
result in distortion in the laminated product. These stresses may be attributed to:
– uneven tension applied to the reinforcement as it passes through the treater (resin
impregnator);
– uneven or non-uniform thickness of resin across the reinforcement sheet width;
– improper curing (polymerization) of the resin, that is, under or over cure at the B-stage.
4.1 .4 Lamination
Non-uniform laminating pressure and temperature builds in stresses. Unbalanced construction,
i.e. plies which are out of alignment in the X and Y directions will cause stresses to be present.
Foil on one side only of a laminate can make any distortion worse. The thicker the foil, the
greater will be the distortion. In addition, when one side of a laminate is clad with thicker foil
than the other, distortion can result.
4.1 .5 Cutting and handling
Cutting methods can induce stress. Storage of the finished material other than in the horizontal
plane can cause distortion.
IEC 61188-1-1:1997 pdf download
