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+44(0)1822
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24 934 125 |
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info@aci-ecotec.co.uk |
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info@aci-ecotec.de |
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| Technical notes... |
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| Soldering
Points - Metallurgy |
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| Solderability Table: |
| Category
1- solderable |
Category
2 - conditionally solderable |
Category
3 - poorly solderable |
Category
4 - not solderable |
| Gold |
Zinc |
Aluminium |
Chrome |
| Tin |
Soft steel |
Alu/Cu |
Titan |
| Tin/Lead |
Monel |
Stainless steel |
Silicon |
| Silver |
Copper/Ni |
Chrom/Ni |
Cobalt |
| Copper |
Copper/Be |
Magnesium |
Wolfram |
| Brass |
Spring Steel |
Cast iron |
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| Copper/tin |
Platinum |
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| Nickel |
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| Cadmium |
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| Category
1: |
Solderable by use of halogen-free
flux |
| Category
2: |
Conditionally solderable by use of
aggressive flux material e.g, zinc chloride solution |
| Category
3: |
Very difficult to solder only after
pre-treatment and with special flux material |
| Category
4: |
not solderable |
|
| Fig 1: Solderability table |
Basically, the parts to be soldered should be pretinned.
If no pretinning has been done, the solderability has
to be tested by attempting to wet a trial piece. The
thicker the tinning, the better. You should try to achieve
a thickness of at least 0.2mm. Silvering also functions
very well as an alternative to tinning. Especially for
higher temperatures caused by the
heating medium (e.g., in the case of induction and flame
soldering), silvering the surfaces is worth recommending.
Gold plated soldering points, on the other hand, have
very low wetting characteristics because the very slight
quantity of gold diffuses (dissolves) and the nickel
underneath has only medium wetting capabilities. Copper
surfaces oxidize very quickly. Therefore, these parts
should be treated within a short period and stored appropriately
(reaction can take place with other materials such as
sulfur).
The general solderability of the individual materials
can be read from the above table (Fig.1)
When contemplating general metallurgical issues, naturally
the question of the solder has to be considered. Although
legislature will be passed, for reasons of environmental
safety, to introduce “non-leaded electronics”
from 2008 onwards, today tin-lead solder is still used
almost exclusively (Sn/Pb solder in accord with DIN
EN 29453). Lead-free solders are already on the market,
or are in the process of development. Up till now, the
production experience with lead-free solder has been
very limited. According to well-known solder manufacturers,
the percentage of lead-free solders used in Germany
is at this time less than 5% of the quantity produced.
For this reason, that which follows refers to the still
customarily used Sn/Pb solders. The solder must always
have a significantly lower melting point
than the material of the parts to be joined. For this
reason, only alloyed solders are used for soft soldering,
whose percentage of Sn or Pb are different, however,
and often compounded with alloying additives. The Sn/Pn
solders have definite advantages that come from the
melting behaviour, the melting temperature range and
the viscosity
• Melting temperature Pb 327.4° C
• Melting temperature Sn 231.8° C
|
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| Fig 2: Phase Diagram - (click image to enlarge) |
The melting temperature of the Sn/Pb solder alloy is
always lower than that of the higher melting Pb component
and reacts in relationship to the alloy ratio. The phase
diagram (Fig. 2) gives information about the melting behavior
of the Sn/Pb solder alloy. Sn/Pn solders reach the so-called
eutectic point at a ratio of 63% Sn and 37% Pb. In this
state, solid us and liquid us occur together, i.e., the
change from solid to liquid happens without transition
at a
temperature of 183°C. Other alloy ratios pass through
a “doey” condition in which one of the alloy
components is fluid and the other is solid (crystalline).
Eutectic solder is advantageous to work with. The solder
temperature is lower than non-eutectic solder and has
good flow
characteristics. It runs thinner, flows faster and fills
fine empty spaces (capillaries). The processing speed
is higher and the texture is finely crystalline and homogenous,
which enhances the durability. Eutectic Sn/Pb solder can
withstand a continuous temperature of
approx. 80° C. An increase of the Pb percentage attains
a higher degree of temperature durability but is less
strong. With a percentage of Pb over 50%, the solder becomes
a lead solder or high temperature solder whose processing
temperature at 95% Pb rises to over 300°. The temperature
for continuous use can be set at 130 - 150° C. A considerably
poorer processing behavior, however, must be taken into
account. Once the soldering cycle is completed, this is
the earliest moment that the soldering point may be placed
under stress mechanically or electrically (electrical
test or work piece movement).
The soldering processes using contactless heat transfer
or that use internal heat generation with, however, an
injected primary energy (radiation, induction or resistor
heating) generally follow this principle as well. It is
of great economical concern to keep the time necessary
for the soldering cycle down to a minimum. Thus, the question
is often raised concerning what possibilities there are
to optimize the time. The temperature/time diagram of
a soldering point can, within certain limits, be varied,
influenced and thereby be optimized from an economical
point of view. The following table (Fig. 3) gives information
about various measures that offer advantages and disadvantages
with regard to shortening the cycle time. The limits must
be carefully selected to avoid that a serious negative
factor cancels the advantage you are trying to attain.
The optimal ratios are determined through experiments
made prior to the automation-planning phase. Only the
empirical determination of data and parameters with contemporary
result control leads you to the optimal production ratios.
Every spot soldering point has its own characteristics
and very often its own set of parameters. The chemical
effects of the flux during the thermodynamic processes
are also to be taken into consideration. |
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| Thermodynamic
Fundamentals |
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| 1.
Soldering Definition |
Soldering and welding are metallurgical
joining techniques. The terms denote a material connection that
is based upon molecular connective forces. When welding, the
parts to be connected are melted (welded) into another or connected
to each other while in a pliable, doe-like condition by the
use of force.
Electronics have pervaded practically all areas of our daily
lives and have thus become a supporting column and an essential
technology for technical progress. The creation of conducting
connections
between components or subassemblies is a central task in the
manufacturing of electronic devices. In this regard, soldering
acquires exceeding significance. It is therefore natural that
trained personnel
that are active in electronic development or production are
continually confronted with the topic of connecting technology.
In can be noted from experience, however, that the discipline
of soldering, in theory and in practice, is somewhat neglected
in the highly qualified training of electrical engineers. So
it’s no surprise that companies often experience a deficit
on know-how when it comes to specific questions about soldering
or soldering automation. Especially in the field of automatic
spot soldering, incomplete knowledge leads to unused rationalizing
potential, and expense-reducing resources
remain untapped. But questions on quality and the securing of
continuous production processes also demand detailed knowledge
and expert know-how.
This document should contribute to helping the production specialists
acquire the needed specific knowledge on the subject of automatic
spot soldering, along with the set-up and operation of the ecoSolder
– Soldering system. At the same time, unnecessary theoretical
ballast should be discarded and the main concentration should
be upon practical questions regarding the production technology
itself and the operation of the soldering system. |
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| Spot welding procedures that can
be automated: |
| Automatic iron soldering |
HF induction soldering |
| Mini wave |
Radiation soldering |
| Solder bath soldering |
Hot-gas soldering |
| Micro flame soldering |
Resistance soldering |
| Thermo compression soldering |
Stamp soldering |
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| Soldering
Basics |
The metallurgical soldering joining technology
follows strict physical laws. Just as a body only swims when
it displaces more water than its own body weighs, so can a good
soldering joint only come to be when the physical requirements
are fulfilled. These prerequisites can be subdivided into:
• metallurgical fundamentals
• thermodynamic
fundamentals
• chemical fundamentals
• geometrical
fundamentals
In addition, the requirements of the soldering tools and/or
processes as well as of the automation technology have to be
considered. Looked at this way, soldering is quite a complicated
matter. There are influences and specifications from all fields
to be considered and, at least partially, to be coordinated
in order to achieve the targeted result of a dependable connection.
As a rule, a soldering point must fulfill two requirements:
good electrical conductivity and sufficient, lasting mechanical
durability under the application conditions. The process itself
must ensure that the parts to be joined and the environment
are not damaged, and also no harmful consequences result. |
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| Soldering Points - Metallurgy |
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