Recommanded profile for 0402 & 0201.| 18 June, 2001
What is the recommanded profile for board which consist of 0402 & 0201 comps. to reduce the effect of tomb-stone. Slow ramp rate ? how slow is considered as slow. Soak time 60 or 120 C,at which end should I stick to? what is the best time before reaching peak? Whatis the bst time above reflow should I maintain ?
I have problem where the 0402 chips does not tomb-stone completely. Its appeared like it was a non-wetting conditions with one of the termination lifted slightly above the pad ( about 5 - 10 Deg angle )while the other termination is well soldered/wetted. Does this considered as Tomb-Stone or non-wetting?We put a blame on an old datecodes capacitors ( which is not so old, I believe i.e. 1 1/2 years old).
Out of my curiosity, will high temp setting at 1st zone setting will encourage the oxidations on 0402 terminations? What I mean here is, eventhough ,temperature profile isOK with ramp/slope at about 1 Deg C/sec, but in order to get good 120 deg - 150 deg C, timing, normally the temperature setting at the 1st zone will be set higher, before it was set at lower temp for the soak's zone, thisis the ramp up from room temperature.
The pad design is 25 X 27 with the gap of about 16 mil. Good gap but bad pad size isn't it? I'm maintaining the gap of 16 but the pad is square 22 X 22, is it OK ?
I'm sure all the Experts out there can help me. Inputs are very much appreciated.
Recommanded profile for 0402 & 0201.| 20 June, 2001
I would suggest getting a copy of IPC-SM-782A, Surface Mount Design and Land Pattern Standard, and IPC-7525 Stencil Design Guidelines. My experience is that reflow does not cause tombstoning very often. Pad and land design, paste volume, and placement are the biggest culprits.
When considering paste volume, it is typically a difference in volume from one side of the component to the other. Look at the aspect and area ratios of the stencil to make sure they are correct.