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SMT Process Qualification: What You Need to Know …

ERSA Know-How Transfer Technical Article SMT Process qualification : what You Need to Know Beyond AOI & Co. by Arndt Neues*. This article was published for the first time in the productronic issue 02/01. AOI, X-ray, functional testing all Detectability typical inline testing and inspection Method Good Satisfactory Poor equipment. They allow nearly com- plete monitoring of the production ICT Interruption Too little solder Bent lead Process based on pre-programmed In-Circuit Test Solder bridge Missing component Positioning precision Defective component Fissured joint Entrapped air decision thresholds. One thing is still Component value Cold solder joint done manually, however: the quali- AOI Bent lead Interruption Hidden solder joint fication and improvement of the pro- Automated Placement accuracy Component value Too little solder duction Process .

productronic0201_e.indd 06.08.2001.ne-dy ERSA GmbH Page 2 ting fault phenomena more precisely, this inspection technology must keep pace with the rapid trend towards minia-

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Transcription of SMT Process Qualification: What You Need to Know …

1 ERSA Know-How Transfer Technical Article SMT Process qualification : what You Need to Know Beyond AOI & Co. by Arndt Neues*. This article was published for the first time in the productronic issue 02/01. AOI, X-ray, functional testing all Detectability typical inline testing and inspection Method Good Satisfactory Poor equipment. They allow nearly com- plete monitoring of the production ICT Interruption Too little solder Bent lead Process based on pre-programmed In-Circuit Test Solder bridge Missing component Positioning precision Defective component Fissured joint Entrapped air decision thresholds. One thing is still Component value Cold solder joint done manually, however: the quali- AOI Bent lead Interruption Hidden solder joint fication and improvement of the pro- Automated Placement accuracy Component value Too little solder duction Process .

2 Optical Inspection Solder bridge Entrapped air This article presents an approach Missing component Cold solder joint to comprehensive Process qualifica- X-RAYS Hidden solder joint Polarity Defective component Laminography Too little solder Component value tion given the improvement potential Entrapped air Flux residue in today s inspection environment. Interruption Fissured joint Solder bridge Cold solder joint The idea is simple: if we consider the Missing component production Process , we see that mod- Table 1 Source: An Integrated Test And Inspection Strategy, David M. Mendez, ern production systems are generally SOLECTRON, Texas, IPC Proceedings of APEX, March 2000. capable of manufacturing quality con- stant within a certain tolerance range, may be tarnished.

3 In such cases pro- Available Testing and Inspection by means of correctly adjusted proc- cess engineers were of the opinion that Equipment for Detecting Sources of ess parameters. reliability data such as the PPM indica- Faults Qualifying a production system proves ted a relatively high quality Process . more difficult, however. qualification an erroneous conclusion, as it turned Sources of faults cannot be detected depends on the ability to detect souces out. without knowledge of the Process it- of faults, to register the totality of all pos- self. Take the soldering Process , for sible faults, and to assess the effects of example: these faults. The Goal: Comprehensive Process The current inline testing and inspec- qualification tion procedures are not capable of pre- Insufficient qualification of the Process senting a complete picture of all possible can be the consequence of the inade- Process qualification largely employs faults occurring in the soldering pro- quate detection of the possible causes manual inspection mechanisms gen- cess, as Table 1 shows.

4 For example, of faults. The Process then lies in the erally the microscope. The reliability of cold solder joints, fissured connections borderline area. Merely those faults Process qualification then crucially de- and flux residues remain largely unde- occurring during the setup phase of pends on the tected. According to analyses by Stig the inline equipment can be generally available inspection equipment Oresjo of Agilent Technologies, inade- be taken into account for the Process . and the quate solder joints make up nearly a fifth Faults that are not or cannot be de- inspector s experience. of all soldering faults (Year 1999 Defect tected are potentially dangerous for the Both variables affect the reliability of Level and Fault Spectrum Study).

5 Process , however. The consequence Process qualification and hence the can be early failure of the affected quality of the Process and the prod- The good/poor decision thresholds de- subassembly no rare occurrence, as ucts. fined for the inline inspection equip- unfortunately seen in the past. The As the producer of soldering and in- ment in the setup phase are in turn affected company may suffer financial spection systems, ERSA GmbH has based on incomplete information about loss if the failure is covered by the war- been deeply concerned about these faults. While the classical microscope is ranty, or at least the company s image issues and has sought for solutions. generally used as a support for inspec- ERSA GmbH. Page 1. ERSA Know-How Transfer SMT Process qualification : what You Need to Know Beyond AOI & Co.

6 Ting fault phenomena more precisely, In combination with other systems, the to be comprehensible and reconstruc- this inspection technology must keep ERSASCOPE thus forms a solid basis tible for future decision processes, com- pace with the rapid trend towards minia- for uncovering fault types in the pro- plete documentation of the inspection turisation: greater and greater magni- duction Process to the widest possible results is equally necessary. fication is needed. The resulting new extent. perspectives and types of faults become The Process improvement comprises a challenge even for experienced altogether the steps of fault detection, inspectors. And faults at hidden Process Improvement through Feed- decision (good/poor), analysis, Process solder joints are hardly ana- back the Inspector s Experience modification, documentation and chek- lysable even when detected by king.

7 Deming already graphically repre- X-rays. They remain inacces- There remains the second issue noted sented this concept in the middle of the sible and hence unviewable above the inspector s experi- last century (Fig. 3). Klein Wassink except by means of cross ence. Every wrong decision & Verguld analogously state the sectioning a time-consu- by the inspector means requirements in their work on Manufac- ming method that can reduced profitability, either turing Techniques for Surface Mounted be applied only sporadi- because the failure to detect Assemblies as follows: no inspection cally. faults leads to defective without documentation, no documenta- goods being prodced, or tion without analysis, no analysis wit- ERSA supple- because there is a high hout action.

8 But what does the practical ments the range of rejection rate for subas- approach look like for the SMT pro- inspection tools with the semblies with non-critical cess? ERSASCOPE System 3000 defects. Repairs are costly, as (Fig. 1 in the top). The 90 optics is the manufacturer s reputation. The Taking the soldering Process as an of the system allows viewing of areas inspector thus bears a burden that example, we encounter an immense on the electronic subassembly that in should be alleviated. The subjective range of distinctive soldering faults. the past were hardly accessible opti- dimension of the decision-making pro- Their structure, form, colour, etc. vary cally. The scope of performance inclu- cess must be brought under control, enormously.

9 In particular with the sol- des both the consideration of hidden if that Process is to be objectively der balls of the BGAs and flip chips, solder joints and the inspection of solder assessed. the hidden solder joints, a criteria tree deposits through side views. The device cannot be set up without undue expen- can thus display faults not detectable Inspection has basically just one goal: diture that would allow automation of by other procedures. Moreover, it is an Process improvement. Inspection as- analysis. indispensable aid for graphically repre- sures that the current status quo of the The approach by ERSA GmbH with senting suspected problems indicated Process is coupled to the tasksetting of the quality assurance software for pro- by the other procedures.

10 Fig. 2 shows Process improvement and hence qua- cess qualification , ImageDoc , opts a few ERSASCOPE images of faults lity improvement for the Process in the for decision-making supported by the detected by X-rays. future. And since this step is supposed following software structure: A. B. X-ray image of PBGA 225: A and B show A. ERSASCOPE reveals flux residue bridge B. ERSASCOPE shows incomplete solder melt mistakes but are unclear of source with conductive particles of paste. Fig. 2: X-ray image and explanatory ERSASCOPE views ERSA GmbH. Page 2 ERSA Know-How Transfer SMT Process qualification : what You Need to Know Beyond AOI & Co. The inspector retrieves good/poor ex- amples, or reference images, stored in Stabilize the Process Recognize the problem the system for the element under in- Standardize Improvements Analyze the Causes spection (Fig.)


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