Printed Circuit Board Assembly & PCB Design SMT Electronics Assembly Manufacturing Forum

Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.


Microcracking in SMT Pick&Place process

Toni Casas i Pujadas

#15452

Microcracking in SMT Pick&Place process | 13 June, 1998

We are very concerned about microcracking in SMT P&P process. I want to know something about: What is microcracking? When did it occur? What are the causes? How can avuid this phenomena?

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Justin Medernach

#15453

Re: Microcracking in SMT Pick&Place process | 16 June, 1998

| We are very concerned about microcracking in SMT P&P process. I want to know something about: | What is microcracking? | When did it occur? What are the causes? | How can avuid this phenomena? Toni, Micro cracks can be caused by a ton of conditions. I'll list a few: 1.) Excessive pick force 2.) Excessive Placement force 3.) Improperly located support pins 4.) Rapid ramp in profile 5.) Entrapped moisture outgassing 6.) Excessive, design related, mechanical stress those are a few. Are you seeing the problem or are you just worried about it. Best advice I can give you is to make sure your reflow and wave profiles are good. Make sure you have board support templates on double sided assemblies so as to avoid placing support pins directly under passive components. I see resistors cracked because of this all the time. When the problem arises, don't put it off. Analyze the problem immedeately. Remember, a microscope is a great tool here!! Regards, Justin Medernach

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Russ Miculich

#15454

Re: Microcracking in SMT Pick&Place process | 25 June, 1998

The real causes of microcracking are not normally due to pick and place - particularly if you are using a piece of equipment with vacuum pick up and release. The real cause of microcracking is due to thermal stresses on the die and the choice of the proper adhesive use to mount the die in the package. The thermal coefficients of expansion mismatches are what cause a majority of the microcracking problem. Microcracking is just what is says --- a fracture line that causes the circuitry of the chip to malfunction through an "open" condition. Microcracking is not easy to detect and can often be an intermittent condition. X-ray and Ultrasound testing are about the only ways to detect it once the die is in and the package is sealed or potted. If you have any further questions or want to discuss this problem related to adhesives and temperatures, don't hesitate to email me. end of line | | We are very concerned about microcracking in SMT P&P process. I want to know something about: | | What is microcracking? | | When did it occur? What are the causes? | | How can avuid this phenomena? | Toni, | Micro cracks can be caused by a ton of conditions. I'll list a few: | 1.) Excessive pick force | 2.) Excessive Placement force | 3.) Improperly located support pins | 4.) Rapid ramp in profile | 5.) Entrapped moisture outgassing | 6.) Excessive, design related, mechanical stress | those are a few. Are you seeing the problem or are you just worried about it. Best advice I can give you is to make sure your reflow and wave profiles are good. Make sure you have board support templates on double sided assemblies so as to avoid placing support pins directly under passive components. I see resistors cracked because of this all the time. When the problem arises, don't put it off. Analyze the problem immedeately. Remember, a microscope is a great tool here!! | Regards, | Justin Medernach

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