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Surface Mount Technology Tips and Quizes
Test your understanding of SMT with the questions below. If you have trouble answering some of the questions, you may benefit from courses taught by Mr. Ray Prasad.
A: QUESTIONS ON SMT OVERVIEW:
1. For what do the following acronyms stand?
2. Indicate which of the SMT board Types (I, II, III) typically makes use of each of the following components and processes: (circle as many as apply)
3. A manufacturing facility has the capability of producing Type II SMT assemblies. What additional equipment is necessary to produce Type I assemblies?
4. Another manufacturing facility has full THMT production capability plus a pick-and-place machine (with adhesive dispensing), and an infrared oven. What SMT assembly types is it capable of producing?
5. On a Type II board, which are placed first on the primary side: SMT devices or THMT devices? Why?
6. What is the biggest problem with larger body surface mount packages?
7. What is the PRIMARY function of the adhesive used in Type II and III assembly?
8. List some of the key elements of strong internal infrastructure. Why does a company need its own unique DFM and Process documents?
9. What are some of the reasons that will keep us in through hole technology for some time to come?
10. Which way should the colored side a chip resistor face? Why?
11. What does the resistor designation 1206 mean? and 1825?
12. What is the difference between Japanese (EIAJ) and American (JEDEC) standard fine pitch packages?
13. Is there one particular lead configuration better than other? Why? Which direction are we headed?
14. List at least five major features of a Pick and Place Machine.
15. What are some of the common problems subcontracting PCAs? a) Quality, b) Delivery, c) Both quality and delivery. What can be done to address these issues?
16. What are the reasons for going to a Subcontract Manufacturer?
17. Name some of the advanced packaging technologies
18. What is KGD?
19. Why has TAB not really taken off?
20. Where does flip chip technology really makes sense?
21. Why and when do you need to consider MCM?
B: QUESTIONS ON SMT DESIGN:
1. What are some of the driving forces for SMT?
2. How does hole size and layer count affect the cost of PCB? Why?
3. Why would you want to use "Loose Packaging"?
4. Is via in pad design acceptable? When and why? When and why not?
5. Which two device types are the major contributors to power consumption (and heat dissipation) on typical boards?
6. What can be done to prevent thermal problems?
7. What percent of real estate is generally wasted in mixed assembly Type II design? And in Type I?
8. What causes plastic package cracking? List some of the MAJOR contributing factors.
9. How can plastic package cracking be prevented? Is there an industry standard available? If yes, please list their names.
10. Why isn't moisture-induced package cracking a problem for plastic DIPs? Why is it even a bigger problem for BGA?
11. What is the key impact of BGAs on board design?
12. Which is the preferred design approach for BGA- NSDM or SMD pad? Why?
13. What is the major problem in using LCCCs? Have they been solved by the industry?
14. What are some of the common defects caused by poor land pattern design?
15. In land pattern design for the following device types, is the major fillet the inner one or the outer one?
16. For a given component, if both wave and reflow soldering can process it, is it a good idea to use the same pad designs for both processes? If yes, Why? If not, why?
17. What is the difference between design rule and design guideline? Do we really need both? Why?
18. Of all the DFM rules and guidelines, which one is the most critical DFM rule?
19. What role does a subcontractor play in development of DFM for an OEM? What role should he really play? And how?
20. Why does every company need it own unique internal DFM document? Which industry document is a good starting point? Why is that document not adequate?
21. Why isn't wet soldermask used on Type I board?
22. Why isn't dry film soldermask used on Type II or III boards?
23. Many interpackage spacing guidelines are expressed as pad-to-pad dimensions, rather than lead-to-lead, or body-to-body. When two J-leaded PLCCs are placed next to each other, will the resulting body-to-body dimensions be: (a) greater than pad-to-pad dimensions (b) less than pad-to-pad dimensions
24. What might the impact be of violating interpackage spacing rules?
25. Interpackage spacing rules are independent of the soldering method used (wave solder or reflow solder), because they are related to auto-placement, test, and rework. True/False
26. Since device leads do not protrude through an SMT board, how does a bed-of-nails test fixture contact the board's nodes?
C: QUESTIONS ON SMT MANUFACTURING:
1. How is adhesive applied to the board? What type of process is used to cure adhesive? Does it take less time to cure adhesive in a 10-zone oven than a 4-zone oven?
2. What defects are caused by excess adhesive? Insufficient adhesives?
3. Why should the temperature ramp rate be controlled during adhesive cure?
4. Which is more critical during adhesive cure: Maximum temperature of cure or time at maximum temperature?
5. What is the composition of the most widely used solder in the electronics industry? At what temperature does the solder melt?
6. List some of the common causes of solder balls?
7. How is dewetting differentiated from non-wetting? List the names of industry solderability specs.
8. What is the size distribution of solder paste powder particles in use today? Why was it necessary to change this size distribution for fine pitch technology?
9. Why is it necessary to bring solder paste and adhesive to room temperature before use?
10. Which is most widely used in the industry - Stencils or Screens? Why? Metal Squeegee or Rubber squeegee? Why?
11. What are some of the key features of etched, laser cut and electroformed stencils?
12. When does it make sense to use paste in hole process?
13. What are some of the concerns of paste in hole process
14. When paste in hole process is not feasible?
15. What are the standards for solderability test? Please list their number?
16. What are three different types of IR reflow processes? Which one is most common today? Why?
17. Can only one solder profile be used for all products when using forced convection IR?
18. How should thermal profile be developed?
19. What are some of the major problems in wave soldering?
20. What are the benefits of N2? Can design and process problems be avoided by the use of N2?
21. Why is a nickel barrier important for ceramic chip capacitors?
22. What causes ceramic capacitor cracking?
23. What does "SIR" stand for and what is a SIR Test Pattern? On what Types of boards must SIR test patterns be placed? On what side(s) of those boards?
24. What are some of the key issues with "No Clean" flux and pastes? What are the three methods of cleanliness measurements?
25. What are some of the problems with fine pitch?
26. What changes need to be made when using fine pitch?
27. How does BGA solve some of the problems of fine pitch? What new problems does it create?
28. List some of the common inspection methods
29. Where on the SMT does it make the most sense to inspect?
30. What is preferable? Bridge or an open? Why? What is the recommended ration of bridge to open?
31. What are the concerns in rework?
32. What is the key variable that is critical in preventing problem during rework
33. List the names of industry workmanship standards?
35. Give an example of acceptance requirements that is too loose given the state of the art and equipment available today
36. What is the acceptable limit for lead misalignment on lands for J-leads?
37. Is solder in the bend of a J-lead acceptable? Why not?
Ray Prasad Consultancy Group | 15375 SW Beaverton Creek Court | Beaverton, OR 97006 USA |