What are mian Reasons for Cracks in BGA Soldering

2019-12-14 14:44Writer: qyadminReading:

 soldering bga ic on pcb

 
      BGA Soldering and Repairing of Ball Grid Array is different. and difficult from SMD soldering and desoldering.
 
      Electronic Devices and Gadgets are getting smaller and slimmer day by day. All this is possible because of technological progress and development in electronics. Top Electronic Companies in the World are in competition to make the smallest. and slimmest gadgets.
 
      BGA or Ball Grid Array is one type of packaging for Surface Mount Technology. (where SMD electronic components are actually mounted or affixed. on the surface of the SMT printed circuit board). A BGA package has no leads or pins. The Ball Grid Array gets its name because it is an array of metal alloy balls arranged in a grid. These BGA Balls are Tin/Lead (Sn/Pb 63/37) or Tin/Silver/Copper (Lead-Free).
 
     The PCB or Printed Circuit Board in today’s electronic devices. and gadgets populated with electronic components. The size of the Circuit Board will increase. with increase in number of electronic components. to squeeze the size of the PCB, SMDs and BGA Packages used because both SMD and BGA are smaller. and slimmer in size and occupy very little space on the PCB.
 
      BGA components provide better solution for many Types of PCB, but care required. when soldering BGA components to. ensure that the BGA solder process is correct and is reliable.
 
      During the initial stages, BGA technology was a matter of concern. People had doubts on solderability and reliability of BGA components. In BGA, the pads are under the device and not visible . and hence it is necessary to ensure the correct process of soldering and inspection.
 
      Today, BGA soldering techniques tried and tested. and has proved and trusted to be very reliable. It has also been learnt that once the process is set up. BGA solder reliability is mush higher than that for quad flat packs (QFP) or any other SMD Package.
 

     Modern electronics services happen to be developing towards fine range. and ultra thinness together with applied electronics components becoming more and more smaller. Moreover, a lot more electronics elements. with fine-pitch IC (integrated circuit) presentation are actually. assembled on PCB (printed circuit board), especially BGA (ball grid array). and CSP (chip-scale package) components. Component pitch provides converted from 0. 65mm and 0. 5mm into 0. 4mm or fewer; PCB thickness from one. 6mm and 1. 2mm into 1. 0mm, zero. 8mm or 0. 6mm or less; PCB level count from double part or 8 layers into 12 layers, 18 tiers or more. BGA mounting function from single mounting into POP (package on package). All the development mentioned over has been challenging the PCB manufacturing. and PCBA functions among which. but, soldering quality of BGA is such a crucial factor that BGA breaks are generally caused. as as one procedure obtains insufficient concern or a good unsuitable measure made. the commonest position. where breaks occur on BGAs is usually soldering connection of pad and pad bottom. Generally speaking, cracks take place many at four corners of a BGA component plus . then at its several sides because they suffer from the most stress.
 
        the reasons for causing breaks in BGA soldering. may explained in the following paragraphs.
 
 

       Poor of PCB Leading to BGA Cracks

 
  • Incorrectly-Picked Tg and Td of PCB Substrate Material
 
        During \the process from lead production to lead-free manufacturing, reflow soldering. and wave soldering temperature must rise upward due to SMT (surface mount technology). assembly necessity. Some people \consider it OK that substrate material. with high Tg (glass transition temperature). will selected for PCB panel. They believe that is actually necessary to manage and handle Z-axis expansion. The primary aim is to stop delamination from taking place of thick circuit boards and 14-layer or more PCBs and to stop cracks from taking place to PTH (plated by means of hole) because a huge level of Z-axis expansion of PCB tends to business lead PTH hole wall to during reflow or influx soldering. Nevertheless, Tg does not defeat cracks developed in the course of lead free process except if Td (temperature of de-composition) considered to solve PCB cracks issue. Three levels of Td regulated in IPC on PCB substrate material: 310°C, 325°C and 340°C.
In conclusion, during the process of substrate material determination. the higher Tg and Td are, the better. Nevertheless PCB fabrication cost will be an essential consideration centered on which substrate materials with agreeable Tbesideson to Td should selected up.
 
 

  • Insufficient Skin gels Content in Prepreg

 
  Insufficient gel content in prepreg used on external tiers and between internal layers tends to lead water piping foil to generate pockets under high temperature.
 
 

  • Unsuitable Copper Profile Assortment

 
  Generally, ordinary profile is usually classified into three classes: standard profile, lower user profile and very lower account. Standard profiles contain no regulations on copper page because adhesiveness is higher but too high account tends to cause negative etching, which further decreases stability of line size and impedance control. Reduced profile regulates that best Profile SPEC is zero. 4mil (10. 2μm). Upwards to now, lower account has leveraged by most PCB manufacturers. Very lower profile regulates that maximum Profile SPEC is usually 0. 2mil (5. 1μm), which is generally leveraged in PCB manufacturing with special fine range need such as 2mil trace width.
 
 

  • Low-Performed PCB Laminierung

 
  Whenever low-performed PCB lamination takes spot, insufficient melanism or brownization will result in bad adhesiveness.
 
 

  • Low-Performed Solder Cover up Developing or Surface Finish

 
  Low-performed solder mask building or surface finish may cause soldering defects. For instance , surface oxidation tends to be able to created when OSP film is too thick or too thin, receives improper pre-process or undergoes too long holding time.
 
 
  • Too Small BGA Mat Size
 
       During the design and style phase, when BGA mat dimensions are too small, that takes place credited to over etching or absence of compensation associated with etching factor.
 
 
 Untrusted arriving Material and Layout of BGA
 
  • When base Z-axis expansion of BGA incoming material is also large, it'll feature lower peel-off strength and Td will be too low, the two of which cause tin cracks.
  • Vacuum packaging isn't implemented following IQC (incoming quality control) check, vacuum package suffers from breakage ahead of preparing or BGA adhesive to board surface for more than two hours ahead of soldering, but will lead to bad soldering.
  • During BGA structure, its pad size could never be too tiny and pad size can never be lower as compared to half pitch of BGA minus 2mil, except for pad employed in special circumstances. Moreover, pad on several corners of BGA need to be 1mil larger than their pads of size.
 
 
       • Four corners of BGA had better be designed to be SMD (solder mask define) because the enlarging of BGA base and the occurrence of solder mask cover around pad will dramatically improve crack resistance of pad. As solder mask define soldering is used, soldering can only cover the surface with side overlooked, which leads regarding soldering connection worse than copper mineral define soldering.
  • PCB with ENIG surface finish applied causes cracks at BGA soldering connections more easily. ENIG can never be leveraged on BGA whose pad is 11mil lower and OSP is more agreeable.
  Insufficient Method Control or Low Set up Condition
  • During stencil design phase, four edges and each side of BGA component should be 1mil to 2mil greater than those of mat. Stencil opening size should be designed based on specs of BGA components including pitch, soldering tennis balls on BGA and element of soldering balls.
  • During the process of printing, support pin. should not be against BGA to stop fake soldering and cushion. effect from taking place due to contamination of BGA pad. Furthermore, especially much attention has to paid to printing scraper pressure and printing quality control.
  • Wafer positions of pickup BGA, component density setting and pressure amount of pickup should emphasized during mounting phase.
  • There are more opportunities for cracks during IR reflow and work needs to paid:
  a. Along the way of double-side PCB manufacture, PCB deformation degree needs to considered. Fixtures can applied during reflow soldering. and substrate of fixtures needs to considered for its possible shrinking due to high temperature. and cooling.
  b. Incoming BGA components have to examined to see . whether going does take place on soldering balls. Moreover, metal ingredient of soldering tennis balls and compatibility. between Z-axis expansion of substrate substance of BGA and PCB board.

 

How is BGA work

 
One of the initial fears over the use of BGA components was their solderability and whether soldering BGA components could be made as reliable as soldering devises using more traditional forms of connection. As the pads are under the device and not visible it is necessary to ensure the correct process is used and it is fully optimised. Inspection and rework were also concerns.
 
Fortunately BGA solder techniques have proved to be very reliable, and once the process is set up correctly BGA solder reliability is normally higher than that for quad flat packs. This means that any BGA assembly tends to be more reliable. Its use is thus now widespread in both mass production PCB assembly and also prototype PCB assembly where circuits are being developed.
 
For the BGA solder process, reflow techniques are used. The reason for this is that the whole assembly needs to be brought up to a temperature whereby the solder will melt underneath the BGA components themselves. This can only be achieved using reflow techniques.
 
For BGA soldering, the solder balls on the package have a very carefully controlled amount of solder, and when heated in the soldering process, the solder melts. Surface tension causes the molten solder to hold the package in the correct alignment with the circuit board, while the solder cools and solidifies.
 
The composition of the solder alloy and the soldering temperature are carefully chosen so that the solder does not completely melt, but stays semi-liquid, allowing each ball to stay separate from its neighbours.
 
BGA inspection is one area of the PCB assembly process that has raised a considerable amount of interest when BGAs were first introduced.
 
BGA inspection cannot be achieved in the normal way using straightforward optical techniques because, quite obviously, the solder joints are underneath the BGA components and they are not visible.
 
It created a considerable degree of unease about the technology when it was first introduced and many manufacturers undertook tests to ensure that they were able to solder the BGA components satisfactorily. The main problem with soldering BGA components is that sufficient heat must be applied to ensure that all the balls in the grid melt sufficiently for every BGA solder joint to be satisfactorily made.
 
The solder joints cannot tested by checking the electrical performance. While this form of test of the BGA solder process will reveal conductivity at that time. it does not give a full picture of how the BGA solder process has succeeded. It is possible that the joint may not made and that over time it will fail. For this the only satisfactory means of test is a form of BGA inspection using X-rays.  This form of BGA inspection is able to look through the device at the soldered joint beneath. As a result Automated X-ray Inspection. AXI became a mainstream technology for checking PCB assemblies that included BGAs. it isfound that once the heat profile for the solder machine is set up. the BGA components solder very well. and few problems encountered with the BGA solder process.
 
As might  anticipated. it is not easy to rework BGA assemblies unless the correct equipment is available. If a BGA component suspected as being faulty, then it is possible to remove the device. This achieved by heating the BGA component to melt the solder underneath it.
 
In the BGA rework process, the heating is often achieved in a specialised rework station. This comprises a jig fitted with infrared heater, a thermocouple to. watch the temperature and a vacuum device for lifting the package. Great care needed to ensure that only the BGA heated and removed. Other devices nearby need to affected as little as possible otherwise. they may damaged.
 
BGA technology in general and in particular the BGA soldering process. have proved themselves to be very successful since they were first introduced. They are now an integral part of the PCB assembly process used in most companies for mass production. and for prototype PCB assembly.
 

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