Die attach with solder paste

Sam

We install a lot of die in the SMT room using same process as SMT parts.Water soluble solder paste is used for attachment of die to ceramic and boards.

Biggest problem i found is the adjustment from installing the die in the bonding area. The trained personnel in the bonding area were already in the mindset that the die we use is very easily scratched or damaged. Moving the die attach to SMT/Assembly area bought some process problems i as a process eng. never fathomed.

I will endeavor to list what i consider the major process problems and fixes

1)Mindset, mindset, mindset...... SMT/assembly personnel are use to robust components compared to die.This was probably the biggest hurdle. The SMT operators must now treat all pieces through the SMT room with kid gloves (actually has reduce damaged parts)Our die is staight aluminum oxide and just touching the surface of the die with finger nail through finger cots would leave a mark on the die surface.

2)Training, Training, training..... Each and every case of damgaed die was F.A. (Failure Analysis) and process eng. sat down with leadhands/assembly/supervisors (took a while but our last batch of boards through smt that contained die is now 99.6% yield)

3)Equipment-SMT operators/pick and place machine require the equipment to do the job properly. Plastic tweezers and or air pick up/vacuum tools with special anti scratch nozzles to either place die or postion die out of place.

Special nozzles- on the pick and place machine that won't scratch the die (lighting/reflection is a big factor when placing die on the pick and place machine)

Cleaning baskets-special cleaning baskets were made as boards/ceramic would bounce around during cleaning (pressure of spray washer or dryer on cleaning machine). New baskets keeping the peices from moving around reduced instances of sacratched die dramtically

waffle packs-die received in wrong or oversized waffle packs. This caused errors on the pick and place machine which lead to scratching of the die. Incoming inspection now ensures die is recived in approved waffle packs. Sometimes die were received in oversized waffle packs which lead to die moving every which way in the waffle pack during shipping. These die were then sorted by SMT which lead to polarity problems.

4) Die received damaged already in waffle packs from die vendor (Turned out to be a bigger problem than first though). Implemented more sample die inspection which resulted in a lot of die being sent back to vendor.

5)Handling and documentation-need i say more. Process eng. found die were being damaged during singualtion and inspection.

Assy personnel here more then 20 years were not handling the boards on the edges during inspection or singulation. process eng. Worked with assy. personnel to reduce damaged die during handling than documented this process.

Ownership of the defects/problems is also a must.

Hope these suggestions help ya as I've lived throught them.

There is light at the end of the tunnel!

Jim M.

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