Evaluating Soldering Irons for Lead Free Assembly

Evaluating Soldering Irons for Lead Free Assembly
Evaluating Soldering Irons for Lead Free Assembly - A Quantitative
Approach
Purnanand G. Samant, Srikanth Poranki, & Daryl Santos, Ph.D,
T.J. Watson School of Engineering and Applied Science
Binghamton University
Binghamton, NY
Abstract
Transition to lead free solder stations in electronics packaging has raised issues regarding process, metallurgy and
reliability m assemblies. In regards to soldering, lead has been used for thousands of years in a wide range of applications.
Conventional eutectic or near eutectic tin-lead solder compositions have been used for virtually all soldering applications in
electronics assembly for the last 50 years, In the electronics assembly process, a majority of commercial rework applications and
some low density board assembly processes require hand soldering stations. Managers and operators, alike, are faced with
a decision to make a selection from a suite of commercially available choices wherein cost by itself cannot be the only
deciding factor, Tin-lead soldering Stations have much lower operating temperatures and, with longer tip lives as compared to
those of lead free soldering stations, soldering temperature becomes a significant factor which can impact the quality of
soldering using lead free soldering stations. Apart from differences like the ones mentioned earlier, an evaluation of
soldering stations should also include ergonomic and operational characteristics. To make matters more difficult, there is not a
lot of help in the form of published guidelines that can aid in making this selection. This paper describes an attempt to
quantify both qualitative and quantitative data that can aid in the evaluation of lead free soldering irons.
Introduction
Primarily due to overseas legislative actions, many sectors of the electronics industry need to be lead free starting July ,
2006. This is not just a result of the business strategies or environmental concerns but also a result of market pressures, driven
by mandates from Japan and the EU. As a result of this, soldering equipment needs to be upgraded to lead-free from tin-lead. In the
electronics assembly process, a majority of commercial rework applications and some low density board assembly processes still require
hand soldering stations. Furthermore, many small scale manufacturers assemble low density boards using hand soldering stations.
For decades, operators have been using soldering irons with operating temperatures of little over 183°C (the melting point of
tin-lead solder). Now with the transition to lead-free, the melting point of the solder has increased and the old soldering stations cannot
be used for lead free soldering. Due to higher operating temperatures (~217°C ) with lead-free solders, the process window for
hand soldering has been reduced. It has become increasingly difficult to get good solder joints without burning the boards, components, etc.
Selection of a good soldering station that meets the requirements of a lead free process, that is comfortable to operators, and that does not
burn the boards or components is a major step towards the transition to lead-free.
Managers and operators, alike, are faced with this decision to make a selection of a suitable soldering station from a suite of
commercially available choices wherein cost by itself cannot be the only deciding factor. There are other aspects, like technical
attributes, operational performance, and ergonomics of the operator, among others, on the basis of which the soldering station
should be selected. In this study, an attempt to quantify both qualitative and quantitative data that can help managers in
evaluation of lead free soldering stations is undertaken.
Experimental Setup
The test vehicle used was an IPC standard test board for lead free applications. In this experiment, we have compared the
company's current soldering iron (Soldering Iron I Metcal) to a competing soldering iron (Soldering Iron II Solderite). The soldering
wire used was a silver-copper (SAC) alloy with a composition of 96.5Sn3AgO.5Cu by weight percent and the flux type used was water
soluble. Three operators were chosen to be part of this experiment, each one of the operators was provided with a soldering
station to conduct the experiment. There were an equal number of different types of surface mount and through-hole components.
The operators were already accustomed to one of the soldering irons (Soldering Iron I Metcal) and, since this is a comparative
study, the competing/newer soldering iron (Soldering Iron II Solderite) was compared against the legacy soldering iron A
practice board was also provided to the operators to get accustomed to Soldering Iron II before the actual experiment.
When making decisions, several, criteria are often considered. These criteria include attributes, which can be
measured in economic terms like costs and profits (quantitative), as well as qualitative attributes, such as safety and
ergonomics, which cannot be directly measured with economic values. Therefore, the goal in a multi-attribute decisionmaking experiment should be to identify both objectives and the criteria used in concluding the objective, One of the key
elements Is the choice of the attributes involved, judgment is required to determine the correct number of attributes for the
evaluation. The selection of these attributes is a result of interviews with the operators and managers. The evaluation was
conducted in two phases, a performance attributes based evaluation (PBE) phase and a technical attributes based evaluation
(TBE) phase. During the PBE phase, a questionnaire was provided to the operators and their responses were recorded
regarding their experience with Soldering Iron II. In the TBE phase, technical specifications were collected from the
equipment vendors. The following section summarizes the findings of the comparison,
Results & Discussion
As aforementioned, the evaluation was performed in two phases, the motivation being to accommodate both a
management and an operator point of view in making the selection. During the PBE phase of evaluation, a questionnaire was
developed to include three important categories of equipment evaluation study, a) Ergonomics, b) Operational, and o)
Maintenance, The questionnaire was designed keeping the three categories in mind and a total of 13 questions regarding the
attributes were developed (this is coincidental to the number of attributes in the technical comparison - the TBE and PBE
attributes were independent of each other). The attributes were classified into the above mentioned categories as this study
is an effort to quantify both qualitative and quantitative characteristics of soldering station evaluation. Assigning weights to
attributes was helpful in giving priority to important attributes in a weighted-scoring approach. A questionnaire was used to
quantify attributes and also to facilitate analysis; it was developed based on interviews with operators and managers.
Each of the three operators assigned points to questions, keeping performance of Soldering Iron I (Metcal the legacy
iron) as a basis for comparison. The points assigned were on a scale of 1-5, For example, a score of 4 or 5 was given to
Soldering Iron II (Solderite) if it performs better as compared to Soldering Iron I (Metcal) on a particular attribute, the operators
assigned a score of 3 if it were to be equal in performance to Soldering Iron I for an attribute, or a lower score (1 or 2) if
Soldering Iron I was preferred for that attribute. Based on the weights assigned to the individual attributes, a weighted score
was obtained. Each of the attributes was assigned a particular weight (0-1) based on the importance of the attribute to the
soldering iron evaluation. A higher priority attribute would have higher weights (closer to 1) and lower priority attributes would
have weights (closer to 0) as shown in Table I. Also in Table I, the attributes (Ergonomics, Operational, and Maintenance) are
listed.
Table I Wieghted Scores Of Lead Free Phase for Soldering Iron I
(Metcal)
Operator # 1
Operator # 2
Operator # 3
Score
Score
Score
Weighted 1-5
Weighted 1-5
Weighted
Questions
Weight 1-5
Ergonomics
Is it easier to work with this soldering
station?
0.5
3
1.5
3
1.5
3
1.5
Is it easier to Clean/Replace the Tip?
0.5
3
1.5
3
1.5
3
1.5
What features don’t you like?
0.4
3
1.2
3
1.2
3
1.2
What features do you like?
0.4
3
1.2
3
1.2
3
1.2
Operational
Does this station heat up faster? Do you
like that?
0.6
3
1.8
3
1.8
3
1.8
Does this station perform better soldering
fine pitch?
0.8
3
2.4
3
2.4
3
2.4
Does this station solder faster than the
3
2.1
3
2.1
3
2.1
other?
0.7
Does this station cool faster? Do you like
that?
0.5
3
1.5
3
1.5
3
1.5
Does this station take longer to change
tips?
0.5
3
1.5
3
1.5
3
1.5
Issues with this unit burning boards,
components, etc?
0.7
3
2.1
3
2.1
3
2.1
Is it easier to control temperature with this
station?
0.8
3
2.4
3
2.4
3
2.4
Maintenance
Is it easy to maintain a good working
3
2.1
3
2.1
3
2.1
soldering tip?
0.7
TOTAL SCORE
21.3
21.3
21.3
As this is a comparative evaluation study against a legacy tool for Soldering Iron I, all of the operators assigned a score of 3 to all
attributes in scoring Soldering Iron 1 The comparative evaluation approach was employed in this study as operators were quite
accustomed to using Soldering Iron I in the past and there was no necessity to conduct an experiment using Soldering Iron L Another
important reason being it would have been difficult for the operators to assign points to Soldering Iron n without any comparison.
Hence, Table I was generated based on weights and common score of 21.3 was computed for all three operators.
Table I, the attributes (Ergonomics, Operational, and Maintenance) are listed.
Table II Wieghted Scores Of Lead Free Phase for Soldering Iron II
(Solderite)
Operator # 1
Operator # 2
Operator # 3
Score
Score
Score
Questions
Weights 1-5
Weighted 1-5
Weighted 1-5
Weighted
Ergonomics
Is it easier to work with this soldering station?
0.5
4
1.5
3
1.5
3
1.5
Is it easier to Clean/Replace the Tip?
0.5
3
1.5
3
1.5
3
1.5
What features don’t you like?
0.4
4
1.2
3
1.2
4
1.2
What features do you like?
0.4
5
1.2
5
1.2
5
1.2
Operational
Does this station heat up faster? Do you like
that?
0.6
4
1.8
3
1.8
3
1.8
Does this station perform better soldering fine
3
2.4
3
2.4
3
2.4
pitch?
0.8
Does this station solder faster than the other?
0.7
4
2.1
3
2.1
3
2.1
Does this station cool faster? Do you like
that?
0.5
3
1.5
3
1.5
2
1.5
Does this station take longer to change tips?
0.5
1
1.5
1
1.5
5
1.5
Issues with this unit burning boards,
components, etc?
0.7
5
2.1
3
2.1
3
2.1
Is it easier to control temperature with this
station?
0.8
5
2.4
5
2.4
3
2.4
Maintenance
Is it easy to maintain a good working
4
2.1
3
2.1
3
2.1
soldering tip?
0.7
TOTAL SCORE
27
22.7
23
As expected, each of the operators provided a different score in evaluating Soldering Iron II. The weighted values were
generated for each of the attributes and the total scores for each of the three operators are as tabulated. Evaluation of any equipment or
process is influenced by experience. In this experiment, each of the three operators varied in their level pf expertise in hand soldering.
Weights were assigned based on their experience; the operator with the most experience (Operator I) was assigned a weight of 0.8,
followed by lesser experienced operator (Operator, II) being assigned a weight of 0.5, and the least experienced operator (Operator III)
was assigned 0.3. After using the weights for the operators' experience, a net score for PBE was generated as follows:
Soldering Iron I: 21.3 (0.8+0.5+0.3) = 34.08 (Metcal)
Soldering Iron II: 27 + .08 + 22.7 + 0.5 + 23 + 0.3 = 39.85 (Solderite)
A similar weighting methodology was used in making comparisons using technical specifications during the TBE phase of evaluation
as shown in Tables III & IV. In this phase, a matrix that lists 13 different technical attributes of the soldering irons was generated. The values
for each of the technical attributes were provided by the vendors as shown in Table III
TECHNICAL ATTRIBUTES
Solder Iron II
Solder Iron I
Average cost of soldering rip ($)
10
20
Unit cost ($)
Temperature control Methodology
245
Tip
310
Tip
Temperature stability (+/- °F)
2
2
Auto sleep mode
Yes
No
Temperature Display
No
No
Tip life Warranty
1 week PB Free
1 week PB Free
Method of changing tip
Screw
Pull nut/Pull in
Time to 660°F claim by the Mfg.
6D seconds
150 seconds
Warranty
Quality of soldering
Spare* Availability
1 Year
Very Good
Good
1 Year
Good
Good
Calibration
Required
Not required
Again, each of the technical attributes was assigned a weight from 0-1 on the basis of importance. For example, attributes like
warranty, cost of the equipment, were weighted 0.8 while lesser important attributes like temperature display were weighted as 0.4. The
weights again were assigned based on interviews with management and operators. As mentioned earlier, Soldering Iron I was
allocated a constant score of 3 for all the attributes (as the legacy tool) and the scores for Soldering Iron II (Solderite) were assigned
based on comparison with Soldering Iron I. (Metcal)
Table IV: Table of weighted scores of attributes used in TBE
TECHNICAL ATTRIBUTES
WEIGHT Soldering Iron II (Solderite)
(0-1)
Soldering Iron I (Metcal)
SCORE (1- WEIGHTED
5)
SCORE
5
4
3
WEIGHTED
SCORE
2.4
3.5
3
2.1
3
2,1
3
2.1
0.8
3
2.4
3
2.4
Auto sleep mode
0,6
4
2.4
3
1.8
Temperature Display
0.4
3
1.2
3
1.2
1
3
3
1
3
Method of Changing Tip
0.8
2
1.5
3
2.4
Time to 660 F claim by Mfg.
0.6
5
3
3
1.8
Warranty
0,8
3
2,4
3
2.4
Quality of Soldering
0.8
4
3.2
3
2.4
Spares Availibility
0,7
3
2.1
3
2.1
1
2
2
3
3
Average Cost of Soldering Tip ($)
0.8
Unit cost ($)
0.7
5
Temperature Control Methodology
0.7
Temperature Stability (+/-F)
Tip Life Warranty
Calibration
TOTAL SCORE
'
SCORE (1-5)
32.9
29.1
Table V summarizes the PBE and TBE final weighted scores for each iron and indicates that Soldering Iron II
has outscored Soldering Iron I in both evaluation methodologies, making it the clear winner.
Evaluation Method
Technical Attribute Based
Evaluation CTEE)
Soldering Iron I (Metcal)
29.1
Soldering Iron II
32.9
Performance Attribute Based
Evaluation (PBE)
34.08
39.85
Conclusions
As a result of this evaluation effort, the company has elected to ma Soldering Iran II (Solderite) for its hand-soldering operations and,
thus far, they are very satisfied with the results.
This effort was an effort to quantify qualitative attributes of soldering irons which would aid managers and operators in making
decisions based on scientific principles and multiple attributes rather than solely on pricing, In this research, a systematic scientific
method to evaluate soldering irons has been suggested. By assigning points to attributes, qualitative attributes could be quantified and
having a questionnaire format would aid in collecting data of qualitative attribute.
This type of approach can be easily extended to consider more than two types of soldering stations in the evaluation
process. Furthermore, the questionnaire can also be easily modified to include fewer, or more attributes - weather qualitative or
quantitative.
Assigning weights to attributes based on priorities could help the decision-maker to consider (place more weight on)
important Actors than on nuisance factors which are of lesser importance. As an extension to this study, a design-of
experiments (DOE) approach could be developed in identifying significant factors that influence the decision, thereby non
significant factors could be eliminated. For another approach, that may be of interest to academics, would be to utilize the
Analytic Hierarchy Process (AHP) (see Ref [2] for more information) to determine if the final decision using that approach, is
similar to the approach taken, herein.
In this paper, an unmentioned assumption is that the TBE and PBE final weighted scores for the irons were equally
considered. Thus, since Soldering Iron II (Solderite) outscored Soldering Iron I (Metcal) in each of those phases, then it
was the clear winner. A different situation may possibly have arisen if a soldering iron did not dominate in both the TBE and
PBE final weighted scores. In that situation, each of the TBE and PBE Scores could be assigned weights (according to the
decision maker(s). Then, to determine the winner, each soldering iron could have its overall weighted (in terms of TBE and
PBE) scores determined, For example, assuming TBE and PBE have equal weighting (0.5 and 0.5), the soldering iron scores
(based upon Table V) are as follows, and not coincidentally concur with our previous result (that Soldering Iron II wins);
Soldering Iron I (Metcal): 29.1*0,5 + 34.08*0.5 = 31.59
Soldering Iron II (Solderite); 32.9*0.5 + 39.85*0.5 =36.38
Acknowledgements
The authors are grateful to the Integrated Electronics Engineering Center (IEEC) at Binghamton University, and the
Strategic Partnership for Industrial Resurgence (SPIR) at Binghamton University.
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