LEAD-FREE HAND SOLDERING: NEW TECHNOLOGIES FOR …

1 LEAD-FREE HAND soldering : NEW TECHNOLOGIES FOR ENHANCING. THE WEAKEST LINK IN THE LEAD-FREE REWORK AND REPAIR. PROCESS CONTROL CHAIN. Mark Cannon ERSA GmbH. Wertheim, Germany Bob Klenke ITM Consulting Cedarburg, WI USA. Phil Zarrow ITM Consulting Durham, NH USA. ABSTRACT. With LEAD-FREE mass soldering processes approved and This paper describes a true breakthrough technology in lead- implemented, increased demand is placed on rework and free manual soldering that greatly enhances solder joint repair as a significant challenge that needs to be addressed quality, guarantees process stability and significantly lowers by board level assemblers. Long considered as the weakest operational cost. A case study will be presented that link in the LEAD-FREE process control chain, LEAD-FREE hand illustrates a design-for-experiment to quantify and insure soldering requires rigorous control of the thermal process LEAD-FREE solder joint reliability.

2 The proper selection of given the higher processing temperatures and reduced tools and procedures to conduct a hand soldering skills audit process window. The paradox between higher process and training methodology assessment to quantify the temperatures of LEAD-FREE alloys and the thermal threshold of consistency of rework and repair operator proficiency will electronic components during the rework and repair process be defined. forms the basis of the LEAD-FREE challenge. THERMAL CONTROL. By examining LEAD-FREE hand soldering more closely, it is The paradox between the higher process temperatures known that a repeatable and stable process is dependent required for LEAD-FREE alloys and the narrower thermal solely on three factors: time, temperature and operator threshold of electronic components form the basis of the technique. Time, or the dwell time of the solder iron tip on LEAD-FREE process challenge as shown in Figure 1.

3 It is for the solder joint, and technique are dependent on operator this reason that there is a greater need for increased thermal skill and training. Temperature however, is governed by the stability and repeatability during the hand soldering and actual temperature of the solder iron tip during the soldering rework and repair processes. process and is dependent 100% on the technology of the soldering iron. Implementing a greater degree of Tin-Lead = 60 C. repeatability and stability of the hand soldering process are solder Alloy: = 45 C. critical ingredients to implementing a successful rework and repair process and reducing thermally induced component or 183 C 200 C 245 C 260 C. board defects. Minimum process temperature Maximum temperature to to assure complete melting of prevent damage to organic Implementing a successful LEAD-FREE rework and repair SnPb alloy (T eut = 183 C) laminates and passive devices operation, the manual soldering process must be evaluated LEAD-FREE = 30 C.

4 On three levels with respect both to operator and solder iron solder Alloy: = 15 C. related issues; a process control and quality aspect, a stability and repeatability standpoint, as well as from an 217 C 230 C 245 C 260 C. operational cost perspective. Given the fact that many companies already running LEAD-FREE in production volume Minimum process temperature Maximum temperature to are consuming up to one solder tip per day, per operating to assure complete melting of SnAgCu alloy ( Teut = 217 C). prevent damage to organic laminates and passive devices station, at significantly high replacement cost, the operational cost factor has a significant impact in a Figure 1. SnPb and SnAgCu Thermal Process Windows competitive manufacturing environment. Originally published in the SMTA International Conference Proceedings, September 2006 Page 1.

5 In a recent study of board level assemblers actively involved feedback is received from a dissatisfied customer. The with LEAD-FREE implementation, hand soldering was reported potential negative impact to both financial outcome, to be more problematic to implement during the transition to company image and customer relations can reach a breaking LEAD-FREE as compared to LEAD-FREE wave and reflow point if products containing hand soldering defects results in Poor wetting and cold solder joints can occur escapes, field failures and/or product recalls. Implications when lower solder tip temperatures are used, or when flux such as these serve as an impetus to management to sit-up activation is insufficient. Excessive solder tip temperatures and take notice of the importance of hand soldering during also result in de-wetting and thermal damage to circuit the LEAD-FREE transition.

6 Boards and components. Using a correct solder tip temperature with adequate but not excessive heat transfer is THERMAL STABILITY. essential for the creation of reliable solder When examining LEAD-FREE hand soldering more closely, it is known that a repeatable and stable process is dependent MANAGEMENT AWARENESS solely on three factors time, temperature and operator The three main factors that directly affect the quality of technique. The dwell time of the solder iron tip on the LEAD-FREE hand soldering are the selection of capable solder solder joint, and the technique are completely dependent on tools, sufficient training of hand soldering operators, and a operator skill and training. Since the majority of LEAD-FREE management focus on the importance of the hand soldering alloys exhibit decreased wetting characteristics and slower and rework and repair processes.

7 Wetting times in comparison to tin-lead (SnPb) solders, an elongated dwell time is recommended as shown in Figure 2. Senior management of contract electronic manufacturers (CEM) and original equipment manufacturers (OEM). should be aware of, and focused on, all process steps throughout their electronic assembly operation. Typically senior management will focus their attention primarily on major capital investment areas such as screen printing, placement, reflow and wave soldering , as well as test and inspection. Often the importance of manual soldering is overlooked, with hand soldering tool selection and operator equipment and training decisions relegated to lower level line personnel. This oversight can prove to be an invitation to disaster. Figure 2. Theoretical LEAD-FREE Hand soldering Because senior management may not place a high priority Thermal Profile on all aspects of the LEAD-FREE transition, their lack of support to fully fund the necessary re-equipping and re- The temperature of the solder joint however, is governed by training of their production floor to successfully implement the actual temperature of the solder iron tip during the LEAD-FREE hand soldering often presents a critical limitation.

8 soldering process and is dependent 100% on the technology Keeping in mind that hand soldering is an operator of the soldering iron. In reality, the temperature of older dependent process; an inadequately equipped and trained technology soldering irons often overshoots the ideal hand solder technician is, in general, not capable of thermal profile while many operators fail to dwell for correctly guiding the process. It is estimated that only 10- sufficient time as shown in Figure 3. 25% of board level assembly companies implement IPC. certified hand solder training while the remaining companies simply buying solder irons and turning them over to line personnel. Consequently, many third-party rework and repair providers are seeing an increased trend of desperate phone calls from board level assemblers complaining of hand solder rejects such as lifted pads and thermal damage, etc.

9 As they begin to implement LEAD-FREE in volume production. Frequently, the board level assembler requests that the damage be repaired to the affected lot of assembled boards, but fails to identify and rectify the internal problem source within their LEAD-FREE Figure 3. Actual LEAD-FREE Hand soldering Thermal assembly operation. Profile Management will eventually take notice when inferior Implementing a greater degree of repeatability and stability quality hand soldering is reflected in significant dollars during the hand soldering process are critical ingredients to worth of product that cannot be shipped or negative implementing a successful hand soldering process and Originally published in the SMTA International Conference Proceedings, September 2006 Page 2. reducing thermally induced component or board defects. iron technology have enabled companies to meet the Temperature overshoot and insufficient dwell can, and do, demands of LEAD-FREE hand soldering and rework and repair result in inadequate solder joint formation and therefore using a state-of-the-art solder station with new and patent should be eliminated as shown in Figure 4.

10 Pending technology the ERSA i-Con and i-Tool. This innovative new soldering tool utilizes 150-watt micro heating element technology that allows for consistent performance as compared to soldering irons equipped with expensive heating element cartridges. Cognizant of the economics of electronic assembly, this improved technology is available at a lower cost due to the use of exchangeable solder iron tips. The 150-watt micro heating element technology allows for standard, low cost tips that can be removed without replacing the heating element each time a solder tip needs replacement. Thus, a savings can be achieved through the use of this innovative, multiple sensor heating element Figure 4. Comparison of Theoretical and Actual Lead- free Hand soldering Thermal Profiles control technology. This new heating technology allows for rapid heat-up from room temperature to 350 C in How well a solder iron recovers heat or puts back the heat approximately 9 seconds, and from standby to 350 C in lost at the tip as well as the length of time the tip remains on only 3 seconds.