Prototype board with  16MSOP - Page 1
Forum section: electronics / general

author: Faringdon
author_rank: Super Contributor
timestamp: December 23, 2023, 10:09:46 pm
content: Hi,Just deciding whether to use LTC7803 for buck controller , or use a discrete sync buck with CST etc.The LTC7803 is 16MSOP....so it needs hot air and hot plate....our board is double sided, and should we need to replace the LTC7803 during prototype testing, it will be pretty well impossible to do so....we couldnt use a hot plate as there are bottom side components...also, hot air is not really practical, as the board is rammed, and hot air will blow off lots of components.As such, we will use SOIC style current mode controller even though it means separate sync buck gate drive chip and sense transformer........do you agree we are right?LTC7803https://www.analog.com/en/products/ltc7803.html

author: Kean
author_rank: Unknown
timestamp: December 24, 2023, 03:00:14 am
content: I'm guessing you have very little experience with hot air? If done right, you will rarely be blowing off components - and even if you do then you just replace them.And I'd go with a QFN any day over an MSOP package - although I'm still partial to using a SOIC part when I have plenty of space.Otherwise we have no idea about your design requirements, so as usual your question cannot be answered.

author: tooki
author_rank: Super Contributor
timestamp: December 24, 2023, 08:34:04 pm
content: Any professional electronics engineer or technician would know that replacing an MSOP is easy, with multiple ways of doing it, including hot air, low-temp rework solder (ChipQuik), desoldering wire (the untinnable stuff you thread under the legs and then shimmy under as you melt the solder of the legs) and various types of desoldering tools.It remains a mystery why and how this (in)famous OP is able to maintain employment in this field, assuming it’s not a delusion…

author: Faringdon
author_rank: Super Contributor
timestamp: January 05, 2024, 06:05:32 pm
content: Thanks, yes i agree its easy to get off....much more difficult to get back on.

author: tooki
author_rank: Super Contributor
timestamp: January 05, 2024, 07:43:54 pm
content: Nonsense. They’re easy to solder by hand. If you struggle with that, you just need soldering lessons. And flux. Always add flux!

author: ajb
author_rank: Super Contributor
timestamp: January 05, 2024, 11:29:02 pm
content: Quote from: Kean on December 24, 2023, 03:00:14 amYes -- In really challenging situations, you can protect surrounding parts and keep the hot air where you want it by walling off the part to be replaced, either with a protector likethis, or just use some wide kapton to create walls where needed. This is also a good way to protect things like plastic connectors from damage. Temporary solder mask (example) can work well for holding small passives in place that are too close to wall off.Hot air always benefits from a good sticky paste flux, you want something that really stays in place. For installing new parts via hot air, a little dab of flux on the bottom of the part can help, since it brings fresh flux right into the joint as the part is placed on the preheated footprint.